class Signature

Parameter list pattern

class Signature { }

A signature is a static description of the parameter list of a code object. That is, it describes what and how many arguments you need to pass to the code or function in order to call it.

Passing arguments to a signature binds the arguments, contained in a Capture, to the signature.

Signature Literals

Signatures appear inside parentheses after subroutine and method names, on blocks after a -> or <-> arrow, as the input to variable declarators like my, or as a separate term starting with a colon.

sub f($x{ }
#    ^^^^ Signature of sub f 
my method x() { }
#          ^^ Signature of a method 
my $s = sub (*@a{ }
#           ^^^^^ Signature of an anonymous function 
for <a b c> -> $x { }
#              ^^   Signature of a Block 
my ($a@b= 5, (678);
#  ^^^^^^^^ Signature of a variable declarator 
my $sig = :($a$b);
#          ^^^^^^^^ Standalone Signature object 

Signature literals can be used to define the signature of a callback or a closure.

sub f(&c:(Int)) { }
sub will-work(Int{ }
sub won't-work(Str{ }
CATCH { default { put .^name''.Str } };
# OUTPUT: «X::TypeCheck::Binding::Parameter: Constraint type check failed in binding to parameter '&c'␤» 
f(-> Int { 'this works too' } );

Smart matching signatures against a List is supported.

my $sig = :(Int $iStr $s);
say (10'answer'~~ $sig;
# OUTPUT: «True␤» 
my $sub = sub ( Str $sInt $i ) { return $s xx $i };
say $sub.signature ~~ :StrInt );
# OUTPUT: «True␤» 
given $sig {
    when :(StrInt{ say 'mismatch' }
    when :($, $)     { say 'match' }
    default          { say 'no match' }
# OUTPUT: «match␤» 

It matches the second when clause since :($, $) represents a Signature with two scalar, anonymous, arguments, which is a more general version of $sig.

When smart matching against a Hash, the signature is assumed to consist of the keys of the Hash.

my %h = left => 1right => 2;
say %h ~~ :(:$left:$right);
# OUTPUT: «True␤» 

Parameter Separators

A signature consists of zero or more parameters, separated by commas.

my $sig = :($a@b%c);
sub add($a$b{ $a + $b };

As an exception the first parameter may be followed by a colon instead of a comma to mark the invocant of a method. The invocant is the object that was used to call the method, which is usually bound to self. By specifying it in the signature, you can change the variable name it is bound to.

method ($a: @b%c{};       # first argument is the invocant 
class Foo {
    method whoami($me:{
        "Well I'm class $me.^name(), of course!"
say Foo.whoami# OUTPUT: «Well I'm class Foo, of course!␤» 

Type Constraints

Parameters can optionally have a type constraint (the default is Any). These can be used to restrict the allowed input to a function.

my $sig = :(Int $aStr $b);
sub divisors(Int $n{ $_ if $n %% $_ for 1..$n };
divisors 2.5;
# ===SORRY!=== Error while compiling: 
# Calling divisors(Rat) will never work with declared signature (Int $n) 

Anonymous arguments are fine too, if a parameter is only needed for its type constraint.

my $sig = :($@%a);              # two anonymous and a "normal" parameter 
$sig = :(IntPositional);          # just a type is also fine (two parameters) 
sub baz(Str{ "Got passed a Str" }

Type constraints may also be type captures.

In addition to those nominal types, additional constraints can be placed on parameters in the form of code blocks which must return a true value to pass the type check

sub f(Real $x where { $x > 0 }Real $y where { $y >= $x }{ }

The code in where clauses has some limitations: anything that produces side-effects (e.g. printing output, pulling from an iterator, or increasing a state variable) is not supported and may produce surprising results if used. Also, the code of the where clause may run more than once for a single typecheck in some implementations.

The where clause doesn't need to be a code block, anything on the right of the where-clause will be used to smart-match the argument against it. So you can also write:

multi factorial(Int $ where 0{ 1 }
multi factorial(Int $x)        { $x * factorial($x - 1}

The first of those can be shortened to

multi factorial(0{ 1 }

i.e., you can use a literal directly as a type and value constraint on an anonymous parameter.

Tip: pay attention to not accidentally leave off a block when you, say, have several conditions:

-> $y where   .so && .name    {}sub one   {} ); # WRONG!! 
-> $y where { .so && .name }  {}sub two   {} ); # OK! 
-> $y where   .so & {}sub three {} ); # Also good 

The first version is wrong and will issue a warning about sub object coerced to string. The reason is the expression is equivalent to ($y ~~ ($ && $; that is "call .so, and if that is True, call .name; if that is also True use its value for smartmatching…". It's the result of (.so && .name) is will be smart-matched against, but we want to check that both .so and .name are truthy values. That is why an explicit Block or a Junction is the right version.

All previous arguments that are not part of a sub-signature in a Signature are accessible in a where-clause that follows an argument. Therefore, the where-clause of the last argument has access to all arguments of a signature that are not part of a sub-signature. For a sub-signature place the where-clause inside the sub-signature.

sub one-of-them(:$a:$b:$c where { $a.defined ^^ $b.defined ^^ $c.defined }{
    $a // $b // $c
say one-of-them(c=>42); # OUTPUT: «42␤» 

Constraining Optional Arguments

Optional arguments can have constraints, too. Any where clause on any parameter will be executed, even if it's optional and not provided by the caller. In that case you may have to guard against undefined values within the where clause.

sub f(Int $aUInt $i? where { !$i.defined or $i > 5 } ) { ... }

Constraining Slurpy Arguments

Slurpy arguments can not have type constraints. A where-clause in conjunction with a Junction can be used to that effect.

sub f(*@a where {$_.all ~~ Int}{ say @a };
CATCH { default { say .^name' ==> '.Str }  }
# OUTPUT: «[42]␤Constraint type check failed in binding to parameter '@a' ...» 

Constraining named Arguments

Constraints against Named arguments apply to the value part of the colon-pair.

sub f(Int :$i){};
f :i<forty-two>;
CATCH { default { say .^name' ==> '.Str }  }
# OUTPUT: «X::TypeCheck::Binding::Parameter ==> Type check failed in binding to parameter '$i'; expected Int but got Str ("forty-two")␤» 

Constraining Defined and Undefined Values

Normally, a type constraint only checks whether the value of the parameter is of the correct type. Crucially, both object instances and type objects will satisfy such a constraint as illustrated below:

say  42.^name;    # OUTPUT: «Int␤» 
say  42 ~~ Int;   # OUTPUT: «True␤» 
say Int ~~ Int;   # OUTPUT: «True␤» 

Note how both 42 and Int satisfy the match.

Sometimes we need to distinguish between these object instances (42) and type objects (Int). Consider the following code:

sub limit-lines(Str $sInt $limit{
    my @lines = $s.lines;
    @lines[0 .. min @lines.elems$limit].join("\n")
say (limit-lines "\n b \n c \n d \n"3).perl# "a \n b \n c \n d " 
say limit-lines Str3;
CATCH { default { put .^name''.Str } };
# OUTPUT: «X::Multi::NoMatch: Cannot resolve caller lines(Str: ); none of these signatures match: 
#     (Str:D $: :$count!, *%_) 
#     (Str:D $: $limit, *%_) 
#     (Str:D $: *%_)» 
say limit-lines "\n b"Int # Always returns the max number of lines 

Here we really only want to deal with string instances, not type objects. To do this, we can use the :D type constraint. This constraint checks that the value passed is an object instance, in a similar fashion to calling its DEFINITE method.

To warm up, let's apply :D to the right hand side of our humble Int example:

say  42 ~~ Int:D;  # OUTPUT: «True␤» 
say Int ~~ Int:D;  # OUTPUT: «False␤» 

Note how only 42 matches Int:D in the above.

Returning to limit-lines, we can now amend its signature to catch the error early:

sub limit-lines(Str:D $sInt $limit{ };
say limit-lines Str3;
CATCH { default { put .^name ~ '--' ~ .Str } };
# OUTPUT: «Parameter '$s' of routine 'limit-lines' must be an object instance of type 'Str', 
#          not a type object of type 'Str'.  Did you forget a '.new'?» 

This is much better than the way the program failed before, since here the reason for failure is clearer.

It's also possible that type objects are the only ones that make sense for a routine to accept. This can be done with the :U type constraint, which checks whether the value passed is a type object rather than an object instance. Here's our Int example again, this time with :U applied:

say  42 ~~ Int:U;  # OUTPUT: «False␤» 
say Int ~~ Int:U;  # OUTPUT: «True␤» 

Now 42 fails to match Int:U while Int succeeds.

Here's a more practical example:

sub can-turn-into(Str $stringAny:U $type{
   return so $string.$type;
say can-turn-into("3"Int);
say can-turn-into("6.5"Int);
say can-turn-into("6.5"Num);
say can-turn-into("a string"Num);
# OUTPUT: True True True False 

Calling can-turn-into with an object instance as its second parameter will yield a constraint violation as intended:

say can-turn-into("a string"123);
# OUTPUT: «Parameter '$type' of routine 'can-turn-into' must be a type object of type 'Any', not an object instance of type 'Int'...» 

For explicitly indicating the normal behaviour, :_ can be used, but this is unnecessary. :(Num:_ $) is the same as :(Num $).

To recap, here is a quick illustration of these type constraints, also known collectively as type smileys:

# Checking a type object 
say Int ~~ Any:D;    # OUTPUT: «False␤» 
say Int ~~ Any:U;    # OUTPUT: «True␤» 
say Int ~~ Any:_;    # OUTPUT: «True␤» 
# Checking an object instance 
say 42 ~~ Any:D;     # OUTPUT: «True␤» 
say 42 ~~ Any:U;     # OUTPUT: «False␤» 
say 42 ~~ Any:_;     # OUTPUT: «True␤» 
# Checking a user-supplied class 
class Foo {};
say Foo ~~ Any:D;    # OUTPUT: «False␤» 
say Foo ~~ Any:U;    # OUTPUT: «True␤» 
say Foo ~~ Any:_;    # OUTPUT: «True␤» 
my $f =;
say $f  ~~ Any:D;    # OUTPUT: «True␤» 
say $f  ~~ Any:U;    # OUTPUT: «False␤» 
say $f  ~~ Any:_;    # OUTPUT: «True␤» 

The Classes and Objects document further elaborates on the concepts of instances and type objects and discovering them with the .DEFINITE method.

Keep in mind all parameters have values; even optional ones have default defaults that are the type object of the constrained type for explicit type constraints. If no explicit type constraint exists, the default default is an Any type object for methods, submethods, and subroutines, and a Mu type object for blocks. This means that if you use the :D type smiley, you'd need to provide a default value or make the parameter required. Otherwise, the default default would be a type object, which would fail the definiteness constraint.

sub divide (Int:D :$a = 2Int:D :$b!{ say $a/$b }
divide :1a, :2b; # OUTPUT: «0.5␤» 

Constraining signatures of Callables

A Callable parameter can be constrained by its signature, by specifying a Signature literal right after the parameter (no whitespace allowed):

sub f(&c:(IntStr))  { say c(10'ten'};
sub g(Int $iStr $s{ $s ~ $i };
# OUTPUT: «ten10␤» 

This shorthand syntax is available only for parameters with the & sigil. For others, you need to use the long version:

sub f($c where .signature ~~ :(IntStr))  { say $c(10'ten'}
sub g(Num $iStr $s{ $s ~ $i }
sub h(Int $iStr $s{ $s ~ $i }
# f(&g); # Constraint type check failed 
f(&h);   # OUTPUT: «ten10␤» 

Constraining Return Types

There are multiple ways to constrain return types on a Routine. All versions below are currently valid and will force a type check on successful execution of a routine.

Nil and Failure are always allowed as return types, regardless of any type constraint. This allows Failure to be returned and passed on down the call chain.

sub foo(--> Int{ Nil };
say foo.perl# OUTPUT: «Nil␤» 

Type captures are not supported.

This form is preferred for several reasons: (1) it can handle constant values while the others can't; (2) for consistency, it is the only form accepted on this site;

The return type arrow has to be placed at the end of the parameter list, with or without a , before it.

sub greeting1(Str $name  --> Str{ say "Hello, $name" } # Valid 
sub greeting2(Str $name--> Str{ say "Hello, $name" } # Valid 
sub favorite-number1(--> 42{        } # OUTPUT: 42 
sub favorite-number2(--> 42{ return } # OUTPUT: 42 

If the type constraint is a constant expression, it is used as the return value of the routine. Any return statement in that routine has to be argumentless.

sub foo(Str $word --> 123{ say $wordreturn}
my $value = foo("hello"); # OUTPUT: hello 
say $value;               # OUTPUT: 123 
# The code below will not compile 
sub foo(Str $word --> 123{ say $wordreturn $word}
my $value = foo("hello");
say $value;

The keyword returns following a signature declaration has the same function as --> with two caveats.

(1) This form is planned for future removal. (2) This form does not work with constant values

    sub greeting(Str $namereturns Str { say "Hello, $name" } # Valid 
    sub favorite-number returns 42 {        } # This will fail. 

of is just the real name of the returns keyword.

    sub foo() of Int { 42 }# Valid 
    sub foo() of 42 {  };    # This will fail. 

This is similar to placing type constraints on variables like my Type $var = 20;, except the $var is a definition for a routine.

    my Int sub bar { 1 };     # Valid 
    my 42 sub bad-answer {};  # This will fail. 

Coercion Type

To accept one type but coerce it automatically to another, use the accepted type as an argument to the target type. If the accepted type is Any it can be omitted.

sub f(Int(Str$want-intStr() $want-str{
    say $want-int.^name ~ ' ' ~ $want-str.^name
f '10'10;
# OUTPUT: «Int Str␤» 
augment class Str { method Date() {} };
sub foo(Date(Str$d{ say $d.^namesay $d };
foo "2016-12-01";
# OUTPUT: «Date␤2016-12-01␤» 

The coercion is performed by calling the method with the name of the type to coerce to, if it exists (e.g. Foo(Bar) coercer, would call method Foo). The method is assumed to return the correct type—no additional checks on the result are currently performed.

Slurpy (A.K.A. Variadic) Parameters

A function is variadic if it can take a varying number of arguments; that is, its arity is not fixed. Therefore, optional, named, and slurpy parameters are variadic. An array or hash parameter can be marked as slurpy by leading asterisk (*) or two leading asterisks (**) or a leading plus (+). A slurpy parameter can bind to an arbitrary number of arguments (zero or more).

These are called "slurpy" because they slurp up any remaining arguments to a function, like someone slurping up noodles.

$ = :($a@b);     # exactly two arguments, where the second one must be Positional 
$ = :($a*@b);    # at least one argument, @b slurps up any beyond that 
$ = :(*%h);        # no positional arguments, but any number of named arguments 
sub one-arg (@)  { }
sub slurpy  (*@) { }
one-arg (567); # ok, same as one-arg((5, 6, 7)) 
slurpy  (567); # ok 
slurpy   567 ; # ok 
# one-arg(5, 6, 7) ; # X::TypeCheck::Argument 
# one-arg  5, 6, 7 ; # X::TypeCheck::Argument 
sub named-names (*%named-args{ %named-args.keys };
say named-names :foo(42:bar<baz># OUTPUT: «foo bar␤» 

Note that positional parameters aren't allowed after slurpy parameters.

# ===SORRY!=== Error while compiling: 
# Cannot put required parameter $last after variadic parameters 

Normally a slurpy parameter will create an Array, create a new Scalar container for each argument, and assign the value from each argument to those Scalars. If the original argument also had an intermediary Scalar it is bypassed during this process, and is not available inside the called function.

Slurpy parameters have special behaviors when combined with some traits and modifiers, as described in the section on slurpy array parameters.

Types of Slurpy Array Parameters

There are three variations to slurpy array parameters.

Each will be described in detail in the next few sections. As the difference between each is a bit nuanced, examples are provided for each to demonstrate how each slurpy convention varies from the others.

Flattened Slurpy

Slurpy parameters declared with one asterisk will flatten arguments by dissolving one or more layers of bare Iterables.

my @array = <a b c>;
my $list := <d e f>;
sub a(*@a)  { @a.perl.say };
a(@array);                 # OUTPUT: «["a", "b", "c"]» 
a(1$list, [23]);       # OUTPUT: «[1, "d", "e", "f", 2, 3]» 
a([12]);                 # OUTPUT: «[1, 2]» 
a(1, [12], ([34], 5)); # OUTPUT: «[1, 1, 2, 3, 4 5]» 
a(($_ for 123));       # OUTPUT: «[1, 2, 3]» 

A single asterisk slurpy flattens all given iterables, effectively hoisting any object created with commas up to the top level.

Unflattened Slurpy

Slurpy parameters declared with two stars do not flatten any Iterable arguments within the list, but keep the arguments more or less as-is:

my @array = <a b c>;
my $list := <d e f>;
sub b(**@b{ @b.perl.say };
b(@array);                 # OUTPUT: «[["a", "b", "c"],]␤» 
b(1$list, [23]);       # OUTPUT: «[1, ("d", "e", "f"), [2, 3]]␤» 
b([12]);                 # OUTPUT: «[[1, 2],]␤» 
b(1, [12], ([34], 5)); # OUTPUT: «[1, [1, 2], ([3, 4], 5)]␤» 
b(($_ for 123));       # OUTPUT: «[(1, 2, 3),]␤» 

The double asterisk slurpy hides the nested comma objects and leaves them as-is in the slurpy array.

Single Argument Rule Slurpy

A slurpy parameter created using a plus engages the "single argument rule", which decides how to handle the slurpy argument based upon context. Basically, if only a single argument is passed and that argument is Iterable, that argument is used to fill the slurpy parameter array. In any other case, +@ works like **@.

my @array = <a b c>;
my $list := <d e f>;
sub c(+@b{ @b.perl.say };
c(@array);                 # OUTPUT: «["a", "b", "c"]␤» 
c(1$list, [23]);       # OUTPUT: «[1, ("d", "e", "f"), [2, 3]]␤» 
c([12]);                 # OUTPUT: «[1, 2]␤» 
c(1, [12], ([34], 5)); # OUTPUT: «[1, [1, 2], ([3, 4], 5)]␤» 
c(($_ for 123));       # OUTPUT: «[1, 2, 3]␤» 

For additional discussion and examples, see Slurpy Conventions for Functions.

Type Captures

Type Captures allow deferring the specification of a type constraint to the time the function is called. They allow referring to a type both in the signature and the function body.

sub f(::T $p1T $p2, ::C){
    # $p1 and $p2 are of the same type T, that we don't know yet 
    # C will hold a type we derive from a type object or value 
    my C $closure = $p1 / $p2;
    return sub (T $p1{
        $closure * $p1;
# The first parameter is Int and so must be the 2nd. 
# We derive the 3rd type from calling the operator that is used in &f. 
my &s = f( /;
say s(2)# 10 / 2 * 2 == 10 

Positional vs. Named

A parameter can be positional or named. All parameters are positional, except slurpy hash parameters and parameters marked with a leading colon :. The latter is called a colon-pair.

$ = :($a);               # a positional parameter 
$ = :(:$a);              # a named parameter of name 'a' 
$ = :(*@a);              # a slurpy positional parameter 
$ = :(*%h);              # a slurpy named parameter 

On the caller side, positional arguments are passed in the same order as the parameters were declared.

sub pos($x$y{ "x=$x y=$y" }
pos(45);                          # OUTPUT: «x=4 y=5» 

In the case of named arguments and parameters, only the name is used for mapping arguments to parameters. If a fat arrow is used to construct a Pair only those with valid identifiers as keys are recognized as named arguments.

sub named(:$x:$y{ "x=$x y=$y" }
named=> 5x => 4);             # OUTPUT: «x=4 y=5» 

It is possible to have a different name for a named parameter than the variable name:

sub named(:official($private)) { "Official business!" if $private }
named :official;

Aliases are also possible that way:

sub alias-named(:color(:$colour), :type(:class(:$kind))) { say $colour ~ " " ~ $kind }
alias-named(color => "red"type => "A");     # both names can be used 
alias-named(colour => "green"type => "B");  # more than two names are ok 
alias-named(color => "white"class => "C");  # every alias is independent 

More use of aliases can be found in sub MAIN

A function with named arguments can be called dynamically, dereferencing a Pair with | to turn it into a named argument.

multi f(:$named{ note &?ROUTINE.signature };
multi f(:$also-named{ note &?ROUTINE.signature };
for 'named''also-named' -> $n {
    f(|($n => rand))                    # OUTPUT: «(:$named)␤(:$also-named)␤» 
my $pair = :named(1);
f |$pair;                               # OUTPUT: «(:$named)␤» 

The same can be used to convert a Hash into named arguments.

sub f(:$also-named{ note &?ROUTINE.signature };
my %pairs = also-named => 4;
f |%pairs;                              # OUTPUT: «(:$also-named)␤» 

A Hash that contains a list may prove problematic when slipped into named arguments. To avoid the extra layer of containers coerce to Map before slipping.

class C { has $.xhas $.yhas @.z };
my %h = <x y z> Z=> (520, [1,2]);
# OUTPUT: « => 5, y => 20, z => [1, 2])␤» 

Optional and Mandatory Parameters

Positional parameters are mandatory by default, and can be made optional with a default value or a trailing question mark:

$ = :(Str $id);         # required parameter 
$ = :($base = 10);      # optional parameter, default value 10 
$ = :(Int $x?);         # optional parameter, default is the Int type object 

Named parameters are optional by default, and can be made mandatory with a trailing exclamation mark:

$ = :(:%config);        # optional parameter 
$ = :(:$debug = False); # optional parameter, defaults to False 
$ = :(:$name!);         # mandatory 'name' named parameter 

Default values can depend on previous parameters, and are (at least notionally) computed anew for each call

$ = :($goal$accuracy = $goal / 100);
$ = :(:$excludes = ['.''..']);        # a new Array for every call 

Dynamic Variables

Dynamic variables are allowed in signatures although they don't provide special behaviour because argument binding does connect two scopes anyway.

Destructuring Parameters

Parameters can be followed by a sub-signature in brackets, which will destructure the argument given. The destructuring of a list is just its elements:

sub first(@array ($first*@rest)) { $first }


sub first([$f*@]) { $f }

While the destructuring of a hash is its pairs:

sub all-dimensions(% (:length(:$x), :width(:$y), :depth(:$z))) {
    $x andthen $y andthen $z andthen True

Pointy loops can also destructure hashes, allowing assignment to variables:

my %hhgttu = (:40life, :41universe, :42everything);
for %hhgttu -> (:$key:$value{
  say "$key → $value";
# OUTPUT: «universe → 41␤life → 40␤everything → 42␤» 

In general, an object is destructured based on its attributes. A common idiom is to unpack a Pair's key and value in a for loop:

for <Peter Paul Merry>.pairs -> (:key($index), :value($guest)) { }

However, this unpacking of objects as their attributes is only the default behavior. To make an object get destructured differently, change its Capture method.


To match against a compound parameter use a sub-signature following the argument name in parentheses.

sub foo(|c(IntStr)){
   put "called with {c.perl}"
# OUTPUT: «called with \(42, "answer")␤» 

Long Names

To exclude certain parameters from being considered in multiple dispatch, separate them with a double semi-colon.

multi sub f(Int $iStr $s;; :$b{ say "$i$s{$b.perl}" };
# OUTPUT: «10, answer, Any␤» 

Capture Parameters

Prefixing a parameter with a vertical bar | makes the parameter a Capture, using up all the remaining positional and named arguments.

This is often used in proto definitions (like proto foo (|) {*}) to indicate that the routine's multi definitions can have any type constraints. See proto for an example.

If bound to a variable arguments can be forwarded as a whole using the slip operator |.

sub a(Int $iStr $s{ say $i.^name ~ ' ' ~ $s.^name }
sub b(|c{ say c.^namea(|c}
# OUTPUT: «Capture␤Int Str␤» 

Parameter Traits and Modifiers

By default, parameters are bound to their argument and marked as read-only. One can change that with traits on the parameter.

The is copy trait causes the argument to be copied, and allows it to be modified inside the routine

sub count-up($x is copy{
    $x = ∞ if $x ~~ Whatever;
    .say for 1..$x;

The is rw trait, which stands for is read-write, makes the parameter bind to a variable (or other writable container). Assigning to the parameter changes the value of the variable at the caller side.

sub swap($x is rw$y is rw{
    ($x$y= ($y$x);

On slurpy parameters, is rw is reserved for future use by language designers.

The is raw trait is automatically applied to parameters declared with a backslash as a "sigil", and may also be used to make normally sigiled parameters behave like these do. In the special case of slurpies, which normally produce an Array full of Scalars as described above, is raw will instead cause the parameter to produce a List. Each element of that list will be bound directly as raw parameter.

To explicitly ask for a read-only parameter use the is readonly trait. Please note that this applies only to the container. The object inside can very well have mutator methods and Perl 6 will not enforce immutability on the attributes of the object.

Traits can be followed by the where clause:

sub ip-expand-ipv6($ip is copy where m:i/^<[a..f\d\:]>**3..39$/{ }


method params

method params(Signature:D: --> Positional)

Returns the list of Parameter objects that make up the signature.

method arity

method arity(Signature:D: --> Int:D)

Returns the minimal number of positional arguments required to satisfy the signature.

method count

method count(Signature:D: --> Real:D)

Returns the maximal number of positional arguments which can be bound to the signature. Returns Inf if there is a slurpy positional parameter.

method returns

Whatever the Signature's return constraint is:

:($a$b --> Int).returns # OUTPUT: «(Int)» 

method ACCEPTS

multi method ACCEPTS(Signature:D: Signature $topic)
multi method ACCEPTS(Signature:D: Capture $topic)
multi method ACCEPTS(Signature:D: Mu \topic)

If $topic is a Signature returns True if anything accepted by $topic would also be accepted by the invocant, otherwise returns False:

:($a$b~~ :($foo$bar$baz?);   # OUTPUT: «True» 
:(Int $n~~ :(Str);                 # OUTPUT: «False» 

The $topic is a Capture, returns True if it can be bound to the invocant, i.e., if a function with invocant's Signature would be able to be called with the $topic:

\(12:foo~~ :($a$b:foo($bar)); # OUTPUT: «True» 
\(1:bar)    ~~ :($a);                 # OUTPUT: «False» 

Lastly, the candidate with Mu topic converts topic to Capture and follows the same semantics as Capture $topic:

<a b c d>  ~~ :(Int $a);      # OUTPUT: «False» 
42         ~~ :(Int);         # OUTPUT: «False» (Int.Capture throws) 
set(<a b>~~ :(:$a:$b);    # OUTPUT: «True» 

Since where clauses are not introspectable, the method cannot determine whether two signatures ACCEPTS the same sort of where-constrained parameters. Such comparisons will return False. This includes signatures with literals, which are just sugar for the where-constraints:

say :(42~~ :($ where 42)    # OUTPUT: «False␤» 

method Capture

Defined as:

method Capture()

Throws X::Cannot::Capture.

Type Graph

Type relations for Signature
perl6-type-graph Signature Signature Any Any Signature->Any Mu Mu Any->Mu

Stand-alone image: vector

Routines supplied by class Any

Signature inherits from class Any, which provides the following methods:

(Any) method ACCEPTS

Defined as:

multi method ACCEPTS(Any:D: Mu $other)



Returns True if $other === self (i.e. it checks object identity).

Many built-in types override this for more specific comparisons

(Any) method any

Defined as:

method any(--> Junction:D)

Interprets the invocant as a list and creates an any-Junction from it.

say so 2 == <1 2 3>.any;        # OUTPUT: «True␤» 
say so 5 == <1 2 3>.any;        # OUTPUT: «False␤» 

(Any) method all

Defined as:

method all(--> Junction:D)

Interprets the invocant as a list and creates an all-Junction from it.

say so 1 < <2 3 4>.all;         # OUTPUT: «True␤» 
say so 3 < <2 3 4>.all;         # OUTPUT: «False␤» 

(Any) method one

Defined as:

method one(--> Junction:D)

Interprets the invocant as a list and creates a one-Junction from it.

say so 1 == (123).one;      # OUTPUT: «True␤» 
say so 1 == (121).one;      # OUTPUT: «False␤» 

(Any) method none

Defined as:

method none(--> Junction:D)

Interprets the invocant as a list and creates a none-Junction from it.

say so 1 == (123).none;     # OUTPUT: «False␤» 
say so 4 == (123).none;     # OUTPUT: «True␤» 

(Any) method list

Defined as:

multi method list(Any:U: -->List)
multi method list(Any:D \SELF: -->List)

Applies the infix , operator to the invocant and returns the resulting List:

say 42.list.^name;           # OUTPUT: «List␤» 
say 42.list.elems;           # OUTPUT: «1␤» 

(Any) method push

Defined as:

method push(|values --> Positional:D)

The method push is defined for undefined invocants and allows for autovivifying undefined to an empty Array, unless the undefined value implements Positional already. The argument provided will then be pushed into the newly created Array.

my %h;
say %h<a>;     # OUTPUT: «(Any)␤»      <-- Undefined 
%h<a>.push(1); # .push on Any 
say %h;        # OUTPUT: «{a => [1]}␤» <-- Note the Array 

(Any) routine reverse

Defined as:

multi sub    reverse(*@list  --> Seq:D)
multi method reverse(List:D: --> Seq:D)

Returns a Seq with the same elements in reverse order.

Note that reverse always refers to reversing elements of a list; to reverse the characters in a string, use flip.


say <hello world!>.reverse;     # OUTPUT: «(world! hello)␤» 
say reverse ^10;                # OUTPUT: «(9 8 7 6 5 4 3 2 1 0)␤» 

(Any) method sort

Defined as:

multi method sort()
multi method sort(&custom-routine-to-use)

Sorts iterables with cmp or given code object and returns a new Seq. Optionally, takes a Callable as a positional parameter, specifying how to sort.


say <b c a>.sort;                           # OUTPUT: «(a b c)␤» 
say 'bca'.comb.sort.join;                   # OUTPUT: «abc␤» 
say 'bca'.comb.sort({$^b cmp $^a}).join;    # OUTPUT: «cba␤» 
say '231'.comb.sort(&infix:«<=>»).join;     # OUTPUT: «123␤» 

(Any) method map

Defined as:

multi method map(\SELF: &block;; :$label:$item)

map will iterate over the invocant and apply the number of positional parameters of the code object from the invocant per call. The returned values of the code object will become elements of the returned Seq.

The :$label and :$item are useful only internally, since for loops get converted to maps. The :$label takes an existing Label to label the .map's loop with and :$item controls whether the iteration will occur over (SELF,) (if :$item is set) or SELF.

(Any) method deepmap

Defined as:

method deepmap(&block --> Listis nodal

deepmap will apply &block to each element and return a new List with the return values of &block, unless the element does the Iterable role. For those elements deepmap will descend recursively into the sublist.

say [[1,2,3],[[4,5],6,7]].deepmap(* + 1);
# OUTPUT: «[[2 3 4] [[5 6] 7 8]]␤» 

(Any) method duckmap

Defined as:

method duckmap(&blockis rw is nodal

duckmap will apply &block on each element and return a new list with defined return values of the block. For undefined return values, duckmap will try to descend into the element if that element implements Iterable.

<a b c d e f g>.duckmap(-> $_ where <c d e>.any { .uc }).say;
# OUTPUT: «(a b C D E f g)␤» 
(('d''e'), 'f').duckmap(-> $_ where <e f>.any { .uc }).say;
# OUTPUT: «((d E) F)␤» 

(Any) method nodemap

Defined as:

method nodemap(&block --> Listis nodal

nodemap will apply &block to each element and return a new List with the return values of &block. In contrast to deepmap it will not descend recursively into sublists if it finds elements which does the Iterable role.

say [[1,2,3], [[4,5],6,7], 7].nodemap(*+1);
# OUTPUT: «(4, 4, 8)␤» 
say [[23], [4, [56]]]».nodemap(*+1)
# OUTPUT: «((3 4) (5 3))␤» 

The examples above would have produced the exact same results if we had used map instead of nodemap. The difference between the two lies in the fact that map flattens out slips while nodemap doesn't.

say [[2,3], [[4,5],6,7], 7].nodemap({.elems == 1 ?? $_ !! slip});
# OUTPUT: «(() () 7)␤» 
say [[2,3], [[4,5],6,7], 7].map({.elems == 1 ?? $_ !! slip});
# OUTPUT: «(7)␤» 

(Any) method flat

Defined as:

method flat(--> Seq:Dis nodal

Interprets the invocant as a list, flattens non-containerized Iterables into a flat list, and returns that list. Keep in mind Map and Hash types are Iterable and so will be flattened into lists of pairs.

say ((12), (3), %(:42a));      # OUTPUT: «((1 2) 3 {a => 42})␤» 
say ((12), (3), %(:42a)).flat# OUTPUT: «(1 2 3 a => 42)␤» 

Note that Arrays containerize their elements by default, and so flat will not flatten them. You can use hyper method call to call .List method on all the inner Iterables and so de-containerize them, so that flat can flatten them:

say [[123], [(45), 67]]      .flat# OUTPUT: «([1 2 3] [(4 5) 6 7])␤» 
say [[123], [(45), 67]]».List.flat# OUTPUT: «(1 2 3 4 5 6 7)␤» 

For more fine-tuned options, see deepmap, duckmap, and signature destructuring

(Any) method eager

Defined as:

method eager(--> Seq:Dis nodal

Interprets the invocant as a List, evaluates it eagerly, and returns that List.

my  $range = 1..5;
say $range;         # OUTPUT: «1..5␤» 
say $range.eager;   # OUTPUT: «(1 2 3 4 5)␤» 

(Any) method elems

Defined as:

method elems(--> Int:Dis nodal

Interprets the invocant as a list, and returns the number of elements in the list.

say 42.elems;                   # OUTPUT: «1␤» 
say <a b c>.elems;              # OUTPUT: «3␤» 

(Any) method end

method end(--> Any:Dis nodal

Interprets the invocant as a list, and returns the last index of that list.

say 6.end;                      # OUTPUT: «0␤» 
say <a b c>.end;                # OUTPUT: «2␤» 

(Any) method pairup

Defined as:

method pairup(--> Seq:Dis nodal

Interprets the invocant as a list, and constructs a list of pairs from it, in the same way that assignment to a Hash does. That is, it takes two consecutive elements and constructs a pair from them, unless the item in the key position already is a pair (in which case the pair is passed through, and the next list item, if any, is considered to be a key again).

say (=> 1'b''c').pairup.perl;     # OUTPUT: «(:a(1), :b("c")).Seq␤» 

(Any) sub exit

Defined as:

sub exit(Int() $status = 0)

Exits the current process with return code $status or zero if no value has been specified. The exit value ($status), when different from zero, has to be opportunely evaluated from the process that catches it (e.g., a shell).

exit does prevent the LEAVE phaser to be executed.

exit should be used as last resort only to signal the parent process about an exit code different from zero, and should not be used to terminate exceptionally a method or a sub: use exceptions instead.

It is worth noting that the only way to return an exit code different from zero from a Main function is by means of using exit.

(Any) sub item

Defined as:

proto sub item(|) is pure
multi item(\x)
multi item(|c)
multi item(Mu $a)

Forces given object to be evaluated in item context and returns the value of it.

say item([1,2,3]).perl;              # OUTPUT: «$[1, 2, 3]␤» 
say item( %apple => 10 ) ).perl;   # OUTPUT: «${:apple(10)}␤» 
say item("abc").perl;                # OUTPUT: «"abc"␤» 

You can also use $ as item contextualizer.

say $[1,2,3].perl;                   # OUTPUT: «$[1, 2, 3]␤» 
say $("abc").perl;                   # OUTPUT: «"abc"␤» 

(Any) method Array

Defined as:

method Array(--> Array:Dis nodal

Coerce the invocant to Array.

(Any) method List

Defined as:

method List(--> List:Dis nodal

Coerce the invocant to List, using the list method.

(Any) method Hash

Defined as:

proto method Hash(|) is nodal
multi method Hash--> Hash:D)

Coerce the invocant to Hash by invoking the method hash on it.

(Any) method hash

Defined as:

proto method hash(|) is nodal
multi method hash(Any:U: --> Hash:D)
multi method hash(Any:D: --> Hash:D)

Creates a new Hash, empty in the case the invocant is undefined, or coerces the invocant to an Hash in the case it is defined.

my $d# $d is Any 
say $d.hash# OUTPUT: {} 
$d.append: 'a''b';
say $d.hash# OUTPUT: {a => b} 

(Any) method Slip

Defined as:

method Slip(--> Slip:Dis nodal

Coerce the invocant to Slip.

(Any) method Map

Defined as:

method Map(--> Map:Dis nodal

Coerce the invocant to Map.

(Any) method Bag

Defined as:

method Bag(--> Bag:Dis nodal

Coerce the invocant to Bag, whereby Positionals are treated as lists of values.

(Any) method BagHash

Defined as:

method BagHash(--> BagHash:Dis nodal

Coerce the invocant to BagHash, whereby Positionals are treated as lists of values.

(Any) method Set

Defined as:

method Set(--> Set:Dis nodal

Coerce the invocant to Set, whereby Positionals are treated as lists of values.

(Any) method SetHash

Defined as:

method SetHash(--> SetHash:Dis nodal

Coerce the invocant to SetHash, whereby Positionals are treated as lists of values.

(Any) method Mix

Defined as:

method Mix(--> Mix:Dis nodal

Coerce the invocant to Mix, whereby Positionals are treated as lists of values.

(Any) method MixHash

Defined as:

method MixHash(--> MixHash:Dis nodal

Coerce the invocant to MixHash, whereby Positionals are treated as lists of values.

(Any) method Supply

Defined as:

method Supply(--> Supply:Dis nodal

Coerce the invocant first to a list by applying the invocant's .list method, and then to a Supply.

(Any) method min

Defined As:

multi method min(--> Any:D)
multi method min(&filter --> Any:D)

Coerces to Iterable and returns the numerically smallest element.

If a Callable positional argument is provided, each value is passed into the filter, and its return value is compared instead of the original value. The original value is still the one returned from min.

say (1,7,3).min();       # OUTPUT:«1␤» 
say (1,7,3).min({1/$_}); # OUTPUT:«7␤» 

(Any) method max

Defined As:

multi method max(--> Any:D)
multi method max(&filter --> Any:D)

Coerces to Iterable and returns the numerically largest element.

If a Callable positional argument is provided, each value is passed into the filter, and its return value is compared instead of the original value. The original value is still the one returned from max.

say (1,7,3).max();       # OUTPUT:«7␤» 
say (1,7,3).max({1/$_}); # OUTPUT:«1␤» 

(Any) method minmax

Defined As:

multi method minmax(--> Range:D)
multi method minmax(&filter --> Range:D)

Returns a Range from the smallest to the largest element.

If a Callable positional argument is provided, each value is passed into the filter, and its return value is compared instead of the original value. The original values are still used in the returned Range.

say (1,7,3).minmax();      # OUTPUT:«1..7␤» 
say (1,7,3).minmax({-$_}); # OUTPUT:«7..1␤» 

(Any) method minpairs

Defined As:

multi method minpairs(Any:D: --> Seq:D)

Calls .pairs and returns a Seq with all of the Pairs with minimum values, as judged by the cmp operator:

<a b c a b c>.minpairs.perl.put# OUTPUT: «(0 => "a", 3 => "a").Seq␤» 
%(:42a, :75b).minpairs.perl.put# OUTPUT: «(:a(42),).Seq␤» 

(Any) method maxpairs

Defined As:

multi method maxpairs(Any:D: --> Seq:D)

Calls .pairs and returns a Seq with all of the Pairs with maximum values, as judged by the cmp operator:

<a b c a b c>.maxpairs.perl.put# OUTPUT: «(2 => "c", 5 => "c").Seq␤» 
%(:42a, :75b).maxpairs.perl.put# OUTPUT: «(:b(75),).Seq␤» 

(Any) method keys

Defined As:

multi method keys(Any:U: --> List)
multi method keys(Any:D: --> List)

For defined Any returns its keys after calling list on it, otherwise calls list and returns it.

say Any.keys# OUTPUT: «()␤» 

(Any) method flatmap

Defined As:

method flatmap(Any:U: &code --> Seq)

Coerces the Any to a list by applying the .list method and uses List.flatmap on it.

say Any.flatmap({.reverse}); # OUTPUT: «((Any))␤» 

In the case of Any, Any.list returns a 1-item list, as is shown.

(Any) method roll

Defined As:

multi method roll(--> Any)
multi method roll($n --> Seq)

Coerces the invocant Any to a list by applying the .list method and uses List.roll on it.

say Any.roll;    # OUTPUT: «(Any)␤» 
say Any.roll(5); # OUTPUT: «((Any) (Any) (Any) (Any) (Any))␤» 

(Any) method pick

Defined As:

multi method pick(--> Any)
multi method pick($n --> Seq)

Coerces the Any to a list by applying the .list method and uses List.pick on it.

say Any.pick;    # OUTPUT: «(Any)␤» 
say Any.pick(5); # OUTPUT: «((Any))␤» 

(Any) method skip

Defined As:

multi method skip(--> Seq)
multi method skip($n --> Seq)

Creates a Seq from 1-item list's iterator and uses Seq.skip on it.

say Any.skip;      # OUTPUT: «()␤» 
say Any.skip(5);   # OUTPUT: «()␤» 
say Any.skip(-1);  # OUTPUT: «((Any))␤» 
say Any.skip(*-1); # OUTPUT: «((Any))␤» 

(Any) method prepend

Defined As:

multi method prepend(--> Array)
multi method prepend(@values --> Array)

Initializes Any variable as empty Array and calls Array.prepend on it.

my $a;
say $a.prepend# OUTPUT: «[]␤» 
say $a;         # OUTPUT: «[]␤» 
my $b;
say $b.prepend(1,2,3); # OUTPUT: «[1 2 3]␤» 

(Any) method unshift

Defined As:

multi method unshift(--> Array)
multi method unshift(@values --> Array)

Initializes Any variable as empty Array and calls Array.unshift on it.

my $a;
say $a.unshift# OUTPUT: «[]␤» 
say $a;         # OUTPUT: «[]␤» 
my $b;
say $b.unshift([1,2,3]); # OUTPUT: «[[1 2 3]]␤» 

(Any) method first

Defined As:

method first(Mu $matcher?:$k:$kv:$p:$end)

Treats the Any as a 1-item list and uses List.first on it.

say Any.first# OUTPUT: «(Any)␤» 

(Any) method unique

Defined As:

method unique(:&as:&with --> Seq:D)

Treats the Any as a 1-item list and uses List.unique on it.

say Any.unique# OUTPUT: «((Any))␤» 

(Any) method repeated

Defined As:

method repeated(:&as:&with --> Seq)

Treats the Any as a 1-item list and uses List.repeated on it.

say Any.repeated# OUTPUT: «()␤» 

(Any) method squish

Defined As:

method squish(:&as:&with --> Seq)

Treats the Any as a 1-item list and uses List.squish on it.

say Any.squish# OUTPUT: «((Any))␤» 

(Any) method permutations

Defined As:

method permutations(--> Seq)

Treats the Any as a 1-item list and uses List.permutations on it.

say Any.permutations# OUTPUT: «(((Any)))␤» 

(Any) method categorize

Defined As:

method categorize(&mapper --> Hash:D)

Treats the Any as a 1-item list and uses List.categorize on it.

say Any.categorize({ $_ }); # OUTPUT: «{(Any) => [(Any)]}␤» 

(Any) method classify

Defined As:

method classify(&mapper -->Hash:D)

Treats the Any as a 1-item list and uses List.classify on it.

say Any.classify({ $_ }); # OUTPUT: «{(Any) => [(Any)]}␤» 

(Any) method produce

(Any) method pairs

Defined As:

multi method pairs(Any:U:  -->List)
multi method pairs(Any:D:  -->List)

Returns an empty List if the invocant is undefined, otherwise converts the invocant to a List via the list method and calls List.pairs on it:

say Any.pairs# OUTPUT: «()␤» 
my $a;
say $a.pairs;  # OUTPUT: «()» 
$a =;
say $a.pairs;  # OUTPUT: «(0 =>» 

(Any) method antipairs

Defined As:

multi method antipairs(Any:U:  -->List)
multi method antipairs(Any:D:  -->List)

Applies the method List.antipairs to the invocant, if it is defined, after having invoked list on it. If the invocant is not defined, it returns an empty List:

my $a;
say $a.antipairs;      # OUTPUT: «()» 
$a =;
say $a.antipairs;      # OUTPUT: «( => 0)» 

(Any) method kv

Defined As:

multi method kv(Any:U:  -->List)
multi method kv(Any:D:  -->List)

Returns an empty List if the invocant is not defined, otherwise it does invoke list on the invocant and then returns the result of List.kv on the latter:

my $a;
say $a.kv;      # OUTPUT: «()» 
$a =;
say $a.kv;      # OUTPUT: «(0» 
say Any.kv;     # OUTPUT: «()␤» 

(Any) method toggle

Defined as:

method toggle(Any:D: *@conditions where .all ~~ Callable:DBool :$off  --> Seq:D)

Iterates over the invocant, producing a Seq, toggling whether the received values are propagated to the result on and off, depending on the results of calling Callables in @conditions:

say ^10 .toggle: * < 4* %% 2&is-prime# OUTPUT: «(0 1 2 3 6 7)␤» 
say ^10 .toggle: :off* > 4;              # OUTPUT: «(5 6 7 8 9)␤» 

Imagine a switch that's either on or off (True or False), and values are produced if it's on. By default, the initial state of that switch is in "on" position, unless :$off is set to a true value, in which case the initial state will be "off".

A Callable from the head of @conditions is taken (if any are available) and it becomes the current tester. Each value from the original sequence is tested by calling the tester Callable with that value. The state of our imaginary switch is set to the return value from the tester: if it's truthy, set switch to "on", otherwise set it to "off".

Whenever the switch is toggled (i.e. switched from "off" to "on" or from "on" to "off"), the current tester Callable is replaced by the next Callable in @conditions, if available, which will be used to test any further values. If no more tester Callables are available, the switch will remain in its current state until the end of iteration.

# our original sequence of elements: 
say list ^10# OUTPUT: «(0 1 2 3 4 5 6 7 8 9)␤» 
# toggled result: 
say ^10 .toggle: * < 4* %% 2&is-prime# OUTPUT: «(0 1 2 3 6 7)␤» 
# First tester Callable is `* < 4` and initial state of switch is "on". 
# As we iterate over our original sequence: 
# 0 => 0 < 4 === True  switch is on, value gets into result, switch is 
#                      toggled, so we keep using the same Callable: 
# 1 => 1 < 4 === True  same 
# 2 => 2 < 4 === True  same 
# 3 => 3 < 4 === True  same 
# 4 => 4 < 4 === False switch is now off, "4" does not make it into the 
#                      result. In addition, our switch got toggled, so 
#                      we're switching to the next tester Callable 
# 5 => 5 %% 2 === False  switch is still off, keep trying to find a value 
# 6 => 6 %% 2 === True   switch is now on, take "6" into result. The switch 
#                        toggled, so we'll use the next tester Callable 
# 7 => is-prime(7) === True  switch is still on, take value and keep going 
# 8 => is-prime(8) === False switch is now off, "8" does not make it into 
#                            the result. The switch got toggled, but we 
#                            don't have any more tester Callables, so it 
#                            will remain off for the rest of the sequence. 

Since the toggle of the switch's state loads the next tester Callable, setting :$off to a True value affects when first tester is discarded:

# our original sequence of elements: 
say <0 1 2># OUTPUT: «(0 1 2)␤» 
# toggled result: 
say <0 1 2>.toggle: * > 1# OUTPUT: «()␤» 
# First tester Callable is `* > 1` and initial state of switch is "on". 
# As we iterate over our original sequence: 
# 0 => 0 > 1 === False  switch is off, "0" does not make it into result. 
#                      In addition, switch got toggled, so we change the 
#                      tester Callable, and since we don't have any more 
#                      of them, the switch will remain "off" until the end 
# our original sequence of elements: 
say <0 1 2># OUTPUT: «(0 1 2)␤» 
# toggled result: 
say <0 1 2>.toggle: :off* > 1# OUTPUT: «(2)␤» 
# First tester Callable is `* > 1` and initial state of switch is "off". 
# As we iterate over our original sequence: 
# 0 => 0 > 1 === False  switch is off, "0" does not make it into result. 
#                       The switch did NOT get toggled this time, so we 
#                       keep using our current tester Callable 
# 1 => 1 > 1 === False  same 
# 2 => 2 > 1 === True   switch is on, "2" makes it into the result 

(Any) method tree

Defined As:

method tree(--> Any)

Returns the class if it's undefined or if it's not iterable, returns the result of applying the tree method to the elements if it's Iterable.

say Any.tree# OUTPUT: «Any␤» 

.tree has different prototypes for Iterable elements.

my @floors = ( 'A', ('B','C', ('E','F','G')));
say @floors.tree(1).flat.elems# OUTPUT: «6␤» 
say @floors.tree(2).flat.elems# OUTPUT: «2␤» 
say @floors.tree*.join("-"), *.join(""), *.join("|" )); # OUTPUT: «A-B—C—E|F|G␤» 

With a number, it iteratively applies tree to every element in the lower level; the first instance will apply .tree(0) to every element in the array, and likewise for the next example.

The second prototype applies the Whatever code passed as arguments to every level in turn; the first argument will go to level 1 and so on. tree can, thus, be a great way to process complex all levels of complex, multi-level, data structures.

(Any) method nl-out

Defined As:

method nl-out(--> Str)

Returns Str with the value of "\n". See for the details.

say OUTPUT: «␤␤» 

(Any) method invert

Defined As:

method invert(--> List)

Returns an empty List.

say Any.invert# OUTPUT: «()␤» 

(Any) method combinations

Defined As:

method combinations(--> Seq)

Treats the Any as a 1-item list and uses List.combinations on it.

say Any.combinations# OUTPUT: «(() ((Any)))␤» 

(Any) method iterator

Defined As:

method iterator(--> Iterator)

Coerces the Any to a list by applying the .list method and uses iterator on it.

my $it = Any.iterator;
say $it.pull-one# OUTPUT: «(Any)␤» 
say $it.pull-one# OUTPUT: «IterationEnd␤» 

(Any) method grep

Defined As:

method grep(Mu $matcher:$k:$kv:$p:$v --> Seq)

Coerces the Any to a list by applying the .list method and uses List.grep on it.

Based on $matcher value can be either ((Any)) or empty List.

my $a;
say $a.grep({ True }); # OUTPUT: «((Any))␤» 
say $a.grep({ $_ });   # OUTPUT: «()␤» 

(Any) method append

Defined As:

proto method append(|) is nodal {*}
multi method append(Any:U \SELF: |values --> Array)

In the case the instance is not a positional-thing, it instantiate it as a new Array, otherwise clone the current instance. After that, it appends the values passed as arguments to the array obtained calling Array.append on it.

my $a;
say $a.append# OUTPUT: «[]␤» 
my $b;
say $b.append((1,2,3)); # OUTPUT: «[1 2 3]␤» 

(Any) method values

Defined As:

method values(--> List)

Returns an empty List.

(Any) method collate

Defined As:

method collate(--> Seq)


(Any) method cache

Defined As:

method cache(--> List)

Provides a List representation of the object itself, calling the method list on the instance.

Routines supplied by class Mu

Signature inherits from class Mu, which provides the following methods:

(Mu) method defined

Declared as

multi method defined(   --> Bool:D)

Returns False on the type object, and True otherwise.

say Int.defined;                # OUTPUT: «False␤» 
say 42.defined;                 # OUTPUT: «True␤» 

Very few types (like Failure) override defined to return False even for instances:

sub fails() { fail 'oh noe' };
say fails().defined;            # OUTPUT: «False␤» 

(Mu) routine defined

Declared as

multi sub    defined(Mu --> Bool:D)

invokes the .defined method on the object and returns its result.

(Mu) routine isa

multi method isa(Mu $type     --> Bool:D)
multi method isa(Str:D $type  --> Bool:D)

Returns True if the invocant is an instance of class $type, a subset type or a derived class (through inheritance) of $type.

my $i = 17;
say $i.isa("Int");   # OUTPUT: «True␤» 
say $i.isa(Any);     # OUTPUT: «True␤» 

A more idiomatic way to do this is to use the smartmatch operator ~~ instead.

my $s = "String";
say $s ~~ Str;       # OUTPUT: «True␤» 

(Mu) routine does

method does(Mu $type --> Bool:D)

Returns True if and only if the invocant conforms to type $type.

my $d ='2016-06-03');
say $d.does(Dateish);             # True    (Date does role Dateish) 
say $d.does(Any);                 # True    (Date is a subclass of Any) 
say $d.does(DateTime);            # False   (Date is not a subclass of DateTime) 

Using the smart match operator ~~ is a more idiomatic alternative.

my $d ='2016-06-03');
say $d ~~ Dateish;                # OUTPUT: «True␤» 
say $d ~~ Any;                    # OUTPUT: «True␤» 
say $d ~~ DateTime;               # OUTPUT: «False␤» 

(Mu) routine Bool

multi sub    Bool(Mu --> Bool:D)
multi method Bool(   --> Bool:D)

Returns False on the type object, and True otherwise.

Many built-in types override this to be False for empty collections, the empty string or numerical zeros

say Mu.Bool;                    # OUTPUT: «False␤» 
say;                # OUTPUT: «True␤» 
say [123].Bool;             # OUTPUT: «True␤» 
say [].Bool;                    # OUTPUT: «False␤» 
say %hash => 'full' ).Bool;   # OUTPUT: «True␤» 
say {}.Bool;                    # OUTPUT: «False␤» 
say "".Bool;                    # OUTPUT: «False␤» 
say 0.Bool;                     # OUTPUT: «False␤» 
say 1.Bool;                     # OUTPUT: «True␤» 
say "0".Bool;                   # OUTPUT: «True␤» 

(Mu) method Capture

Declared as:

method Capture(Mu:D: --> Capture:D)

Returns a Capture with named arguments corresponding to invocant's public attributes:

class Foo {
    has $.foo = 42;
    has $.bar = 70;
    method bar { 'something else' }
}.new.Capture.say# OUTPUT: «\(:bar("something else"), :foo(42))␤» 

(Mu) method Str

multi method Str(--> Str)

Returns a string representation of the invocant, intended to be machine readable. Method Str warns on type objects, and produces the empty string.

say Mu.Str;                     # Use of uninitialized value of type Mu in string context. 

(Mu) routine gist

multi sub    gist(+args --> Str)
multi method gist(   --> Str)

Returns a string representation of the invocant, optimized for fast recognition by humans. As such lists will be truncated at 100 elements. Use .perl to get all elements.

The default gist method in Mu re-dispatches to the perl method for defined invocants, and returns the type name in parenthesis for type object invocants. Many built-in classes override the case of instances to something more specific that may truncate output.

gist is the method that say calls implicitly, so say $something and say $something.gist generally produce the same output.

say Mu.gist;        # OUTPUT: «(Mu)␤» 
say;    # OUTPUT: «␤» 

(Mu) routine perl

multi method perl(--> Str)

Returns a Perlish representation of the object (i.e., can usually be re-evaluated with EVAL to regenerate the object). The exact output of perl is implementation specific, since there are generally many ways to write a Perl expression that produces a particular value

(Mu) method item

method item(Mu \item:is raw

Forces the invocant to be evaluated in item context and returns the value of it.

say [1,2,3].item.perl;          # OUTPUT: «$[1, 2, 3]␤» 
say %apple => 10 ).item.perl# OUTPUT: «${:apple(10)}␤» 
say "abc".item.perl;            # OUTPUT: «"abc"␤» 

(Mu) method self

method self(--> Mu)

Returns the object it is called on.

(Mu) method clone

method clone(*%twiddles)

Creates a shallow clone of the invocant, including shallow cloning of private attributes. Alternative values for public attributes can be provided via named arguments with names matching the attributes' names.

class Point2D {
    has ($.x$.y);
    multi method gist(Point2D:D:{
my $p = => 2=> 3);
say $p;                     # OUTPUT: «Point(2, 3)␤» 
say $p.clone(=> -5);      # OUTPUT: «Point(2, -5)␤» 

Note that .clone does not go the extra mile to shallow-copy @. and %. sigiled attributes and, if modified, the modifications will still be available in the original object:

class Foo {
    has $.foo is rw = 42;
    has &.boo is rw = { say "Hi" };
    has       = <a b>;
    has %.baz       = <a b c d>;
my $o1 =;
with my $o2 = $o1.clone {
    .foo = 70;
    .bar = <Z Y>;
    .baz = <Z Y X W>;
    .boo = { say "Bye" };
# Hash and Array attribute modifications in clone appear in original as well: 
say $o1;    # OUTPUT: « => 42, bar => ["Z", "Y"], baz => {:X("W"), :Z("Y")}, …␤» 
say $o2;    # OUTPUT: « => 70, bar => ["Z", "Y"], baz => {:X("W"), :Z("Y")}, …␤» 
$; # OUTPUT: «Hi␤» 
$; # OUTPUT: «Bye␤» 

To clone those, you could implement your own .clone that clones the appropriate attributes and passes the new values to Mu.clone, for example, via nextwith. Alternatively, your own .clone could clone self first (using self.Mu::clone or callsame) and then manipulate the clone as needed, before returning it.

class Bar {
    has = <a b>;
    has = <a b c d>;
    method clone { nextwith :foo(@!foo.clone:bar(%!bar.clone}
my $o1 =;
with my $o2 = $o1.clone {
    .foo = <Z Y>;
    .bar = <Z Y X W>;
# Hash and Array attribute modifications in clone do not affect original: 
say $o1# OUTPUT: « => ["a", "b"], bar => {:a("b"), :c("d")})␤» 
say $o2# OUTPUT: « => ["Z", "Y"], bar => {:X("W"), :Z("Y")})␤» 

(Mu) method new

multi method new(*%attrinit)

Default method for constructing (create + initialize) new objects of a class. This method expects only named arguments which are then used to initialize attributes with accessors of the same name.

Classes may provide their own new method to override this default.

new triggers an object construction mechanism that calls submethods named BUILD in each class of an inheritance hierarchy, if they exist. See the documentation on object construction for more information.

(Mu) method bless

method bless(*%attrinit --> Mu:D)

Lower-level object construction method than new.

Creates a new object of the same type as the invocant, uses the named arguments to initialize attributes, and returns the created object.

You can use this method when writing custom constructors:

class Point {
    has $.x;
    has $.y;
    multi method new($x$y{
my $p =;

(Though each time you write a custom constructor, remember that it makes subclassing harder).

(Mu) method CREATE

method CREATE(--> Mu:D)

Allocates a new object of the same type as the invocant, without initializing any attributes.

say Mu.CREATE.defined;  # OUTPUT: «True␤» 

(Mu) method print

multi method print(--> Bool:D)

Prints value to $*OUT after stringification using .Str method without adding a newline at end.

"abc\n".print;          # RESULT: «abc␤» 

(Mu) method put

multi method put(--> Bool:D)

Prints value to $*OUT, adding a newline at end, and if necessary, stringifying non-Str object using the .Str method.

"abc".put;              # RESULT: «abc␤» 

(Mu) method say

multi method say(--> Bool:D)

Prints value to $*OUT after stringification using gist method with newline at end. To produce machine readable output use .put.

say 42;                 # OUTPUT: «42␤» 

(Mu) method ACCEPTS

multi method ACCEPTS(Mu:U: $other)

ACCEPTS is the method that smart matching with the infix ~~ operator and given/when invokes on the right-hand side (the matcher).

The Mu:U multi performs a type check. Returns True if $other conforms to the invocant (which is always a type object or failure).

say 42 ~~ Mu;           # OUTPUT: «True␤» 
say 42 ~~ Int;          # OUTPUT: «True␤» 
say 42 ~~ Str;          # OUTPUT: «False␤» 

Note that there is no multi for defined invocants; this is to allow autothreading of junctions, which happens as a fallback mechanism when no direct candidate is available to dispatch to.

(Mu) method WHICH

multi method WHICH(--> ObjAt:D)

Returns an object of type ObjAt which uniquely identifies the object. Value types override this method which makes sure that two equivalent objects return the same return value from WHICH.

say 42.WHICH eq 42.WHICH;       # OUTPUT: «True␤» 

(Mu) method WHERE

method WHERE(--> Int)

Returns an Int representing the memory address of the object.

(Mu) method WHY

multi method WHY(--> Pod::Block::Declarator)

Returns the attached Pod::Block::Declarator.

For instance:

#| Initiate a specified spell normally 
sub cast(Spell $s{
#= (do not use for class 7 spells) 
say &cast.WHY;
# OUTPUT: «Initiate a specified spell normally␤(do not use for class 7 spells)␤» 

See Pod declarator blocks for details about attaching Pod to variables, classes, functions, methods, etc.

(Mu) trait is export

multi sub trait_mod:<is>(Mu:U \type:$export!)

Marks a type as being exported, that is, available to external users.

my class SomeClass is export { }

A user of a module or class automatically gets all the symbols imported that are marked as is export.

See Exporting and Selective Importing Modules for more details.

(Mu) method return

method return()

The method return will stop execution of a subroutine or method, run all relevant phasers and provide invocant as a return value to the caller. If a return type constraint is provided it will be checked unless the return value is Nil. A control exception is raised and can be caught with CONTROL.

sub f { (1|2|3).return };
say f(); # OUTPUT: «any(1, 2, 3)␤» 

(Mu) method return-rw

Same as method return except that return-rw returns a writable container to the invocant (see more details here: return-rw).

(Mu) method emit

method emit()

Emits the invocant into the enclosing supply or react block.

react { whenever supply { .emit for "foo"42.5 } {
    say "received {.^name} ($_)";
# received Str (foo) 
# received Int (42) 
# received Rat (0.5) 

(Mu) method take

method take()

Returns the invocant in the enclosing gather block.

sub insert($sep+@list{
    gather for @list {
        FIRST .takenext;
        take slip $sep.item
say insert ':', <a b c>;
# OUTPUT: «(a : b : c)␤» 

(Mu) routine take

sub take(\item)

Takes the given item and passes it to the enclosing gather block.

#| randomly select numbers for lotto 
my $num-selected-numbers = 6;
my $max-lotto-numbers = 49;
gather for ^$num-selected-numbers {
    take (1 .. $max-lotto-numbers).pick(1);
}.say;    # six random values 

(Mu) routine take-rw

sub take-rw(\item)

Returns the given item to the enclosing gather block, without introducing a new container.

my @a = 1...3;
sub f(@list){ gather for @list { take-rw $_ } };
for f(@a{ $_++ };
say @a;
# OUTPUT: «[2 3 4]␤» 

(Mu) method so

method so()

Returns a Bool value representing the logical non-negation of an expression. One can use this method similarly to the English sentence: "If that is so, then do this thing". For instance,

my @args = <-a -e -b -v>;
my $verbose-selected = any(@argseq '-v' | '-V';
if $ {
    say "Verbose option detected in arguments";
} # OUTPUT: «Verbose option detected in arguments␤» 

(Mu) method not

method not()

Returns a Bool value representing the logical negation of an expression. Thus it is the opposite of so.

my @args = <-a -e -b>;
my $verbose-selected = any(@argseq '-v' | '-V';
if $verbose-selected.not {
    say "Verbose option not present in arguments";
} # OUTPUT: «Verbose option not present in arguments␤» 

Since there is also a prefix version of not, the above code reads better like so:

my @args = <-a -e -b>;
my $verbose-selected = any(@argseq '-v' | '-V';
if not $verbose-selected {
    say "Verbose option not present in arguments";
} # OUTPUT: «Verbose option not present in arguments␤»