class Routine

Code object with its own lexical scope and `return` handling

class Routine is Block { }

A Routine is a code object meant for larger unities of code than Block. Routine is the common superclass for Sub (and therefore operators) and Method, the two primary code objects for code reuse.

Routines serve as a scope limiter for return (i.e. a return returns from the innermost outer Routine).

Routine is also the level at which multiness (multi subs and multi methods) are handled.

Trait is default

There is a special trait for Routines called is default. This trait is designed as a way to disambiguate multi calls that would normally throw an error because the compiler would not know which one to use. This means that given the following two Routines, the one with the is default trait will be called.

multi sub f() is default { say "Hello there" }
multi sub f() { say "Hello friend" }
f();   # OUTPUT: «"Hello there"␤» 

The is default trait can become very useful for debugging and other uses but keep in mind that it will only resolve an ambiguous dispatch between two Routines of the same precedence. If one of the Routines are narrower than another, then that one will be called. For example:

multi sub f() is default { say "Hello there" }
multi sub f(:$greet{ say "Hello " ~ $greet }
f();   # "Use of uninitialized value $greet..." 

In this example, the multi without is default was called because it was actually narrower than the Sub with it.

Methods

method name

method name(Routine:D: --> Str:D)

Returns the name of the sub or method.

method package

method package(Routine:D:)

Returns the package in which the routine is defined.

method multi

method multi(Routine:D: --> Bool:D)

Returns True if the routine is a multi sub or method. Note that the name of a multi sub refers to its proto and this method would return false if called on it. It needs to be called on the candidates themselves:

multi foo ($, $) {};
say &foo.multi;             # OUTPUT: «False␤» 
say &foo.candidates».multi# OUTPUT: «(True)␤» 

method candidates

method candidates(Routine:D: --> Positional:D)

Returns a list of multi candidates, or a one-element list with itself if it's not a multi

method cando

method cando(Capture $c)

Returns a possibly-empty list of candidates that can be called with the given Capture, ordered by narrowest candidate first. For methods, the first element of the Capture needs to be the invocant:

.signature.say for "foo".^can("comb")[0].cando: \(Cool"o");
# OUTPUT: «(Cool $: Str $matcher, $limit = Inf, *%_)␤» 

method wrap

method wrap(Routine:D: &wrapper --> WrapHandle:D)

Wraps (i.e. in-place modifies) the routine. That means a call to this routine first calls &wrapper, which then can (but doesn't have to) call the original routine with the callsame, callwith, nextsame and nextwith dispatchers. The return value from the routine is also the return value from the wrapper.

wrap returns a WrapHandle, which you can pass to unwrap to restore the original routine.

method unwrap

method unwrap(Routine:D: WrapHandle $wraphandle)

Restores the original routine after it has been wrapped with wrap.

method yada

method yada(Routine:D: --> Bool:D)

Returns True if the routine is a stub

say (sub f() { ... }).yada;      # OUTPUT: «True␤» 
say (sub g() { 1;  }).yada;      # OUTPUT: «False␤» 

trait is cached

multi sub trait_mod:<is>(Routine $r:$cached!)

NOTE: this feature is currently EXPERIMENTAL.

Causes the return value of a routine to be stored, so that when subsequent calls with the same list of arguments are made, the stored value can be returned immediately instead of re-running the routine.

Useful when storing and returning the computed value is much faster than re-computing it every time, and when the time saving trumps the cost of the use of more memory.

Even if the arguments passed to the routine are "reference types" (such as objects or arrays), then for the purpose of caching they will only be compared based on their contents. Thus the second invocation will hit the cache in this case:

say foo( [123] );   # runs foo 
say foo( [123] );   # doesn't run foo, uses cached value 
use experimental :cached;
 
sub nth-prime(Int:D $x where * > 0is cached {
    say "Calculating {$x}th prime";
    return (2..*).grep(*.is-prime)[$x - 1];
}
 
say nth-prime(43);
say nth-prime(43);
say nth-prime(43);

produces this output:

Calculating 43th prime
191
191
191

trait is pure

multi sub trait_mod:<is>(Routine $r:$pure!)

Marks a subroutine as pure, that is, it asserts that for the same input, it will always produce the same output without any additional side effects.

This is a promise by the programmer to the compiler that it can constant-fold calls to such functions when the arguments are known at compile time.

sub double(Numeric:D $xis pure {
    2 * $x;
}

trait is rw

multi sub trait_mod:<is>(Routine $r:$rw!)

When a routine is modified with this trait, its return value will be writable. This is useful when returning variables or writable elements of hashes or arrays, for example:

sub walk(\thing*@keysis rw {
    my $current := thing;
    for @keys -> $k {
        if $k ~~ Int {
            $current := $current[$k];
        }
        else {
            $current := $current{$k};
        }
    }
    $current;
}
 
my %hash;
walk(%hash'some''key'12= 'autovivified';
 
say %hash.perl;

produces

("some" => {"key" => [Any, [AnyAny"autovivified"]]}).hash

Note that return marks return values as read only; if you need an early exit from an is rw routine, you have to use return-rw instead.

trait is export

multi sub trait_mod:<is>(Routine $r:$export!)

Marks a routine as exported to the rest of the world

module Foo {
    sub double($x) is export {
        2 * $x
    }
}

import Foo;         # makes sub double available
say double 21;      # 42

From inside another file you'd say use Foo; to load a module and import the exported functions.

See Exporting and Selective Importing Modules for more details.

trait is DEPRECATED

multi sub trait_mod:<is>(Routine:D $r:$DEPRECATED!)

Marks a routine as deprecated, optionally with a message what to use instead.

This code

sub f() is DEPRECATED('the literal 42'{ 42 }
say f();

produces this output:

42
Saw 1 occurrence of deprecated code.
================================================================================
Sub f (from GLOBALseen at:
  deprecated.p6line 2
Please use the literal 42 instead.
--------------------------------------------------------------------------------
Please contact the author to have these occurrences of deprecated code
adaptedso that this message will disappear!

trait is hidden-from-backtrace

multi sub trait_mod:<is>(Routine:D:$hidden-from-backtrace!)

Hides a routine from showing up in a default backtrace. For example

sub inner { die "OH NOEZ" };
sub outer { inner() };
outer();

produces the error message and backtrace

OH NOEZ
  in sub inner at bt.p6:1
  in sub outer at bt.p6:2
  in block <unit> at bt.p6:3

but if inner is marked with hidden-from-backtrace

sub inner is hidden-from-backtrace { die "OH NOEZ" };
sub outer { inner() };
outer();

the error backtrace does not show it:

OH NOEZ
  in sub outer at bt.p6:2
  in block <unit> at bt.p6:3

Type graph

Type relations for Routine
perl6-type-graph Routine Routine Block Block Routine->Block Mu Mu Any Any Any->Mu Callable Callable Code Code Code->Any Code->Callable Block->Code Method Method Method->Routine Macro Macro Macro->Routine Sub Sub Sub->Routine Submethod Submethod Submethod->Routine Regex Regex Regex->Method

Stand-alone image: vector

Routines supplied by class Code

Routine inherits from class Code, which provides the following methods:

(Code) method ACCEPTS

multi method ACCEPTS(Code:D: Mu $topic)

Usually calls the code object and passes $topic as an argument. However, when called on a code object that takes no arguments, the code object is invoked with no arguments and $topic is dropped. The result of the call is returned.

(Code) method arity

Defined as:

method arity(Code:D: --> Int:D)

Returns the minimum number of positional arguments that must be passed in order to call the code object. Any optional or slurpy parameters in the code object's Signature do not contribute, nor do named parameters.

sub argless() { }
sub args($a$b?{ }
sub slurpy($a$b*@c{ }
say &argless.arity;             # OUTPUT: «0␤» 
say &args.arity;                # OUTPUT: «1␤» 
say &slurpy.arity;              # OUTPUT: «2␤» 

(Code) method count

Defined as:

method count(Code:D: --> Real:D)

Returns the maximum number of positional arguments that may be passed when calling the code object. For code objects that can accept any number of positional arguments (that is, they have a slurpy parameter), count will return Inf. Named parameters do not contribute.

sub argless() { }
sub args($a$b?{ }
sub slurpy($a$b*@c{ }
say &argless.count;             # OUTPUT: «0␤» 
say &args.count;                # OUTPUT: «2␤» 
say &slurpy.count;              # OUTPUT: «Inf␤» 

(Code) method signature

Defined as:

multi method signature(Code:D: --> Signature:D)

Returns the Signature object for this code object, which describes its parameters.

sub a(Int $oneStr $two{};
say &a.signature# OUTPUT: «(Int $one, Str $two)␤» 

(Code) method Str

Defined as:

multi method Str(Code:D: --> Str:D)

Will produce a warning. Use .perl or .gist instead.

sub marine() { }
say ~&marine;    # OUTPUT: «marine␤» 
say &marine.Str# OUTPUT: «marine␤» 

(Code) method file

Defined as:

method file(Code:D: --> Str:D)

Returns the name of the file in which the code object was declared.

say &infix:<+>.file;

(Code) method line

Defined as

method line(Code:D: --> Int:D)

Returns the line number in which the code object was declared.

say &infix:<+>.line;

Methods supplied by role Callable

Routine inherits from class Code, which does role Callable, which provides the following methods:

(Callable) method CALL-ME

method CALL-ME(Callable:D $self: |arguments)

This method is required for postfix:«( )» and postfix:«.( )». It's what makes an object actually call-able and needs to be overloaded to let a given object act like a routine. If the object needs to be stored in a &-sigiled container, is has to implement Callable.

class A does Callable {
    submethod CALL-ME(|c){ 'called' }
}
my &a = A;
say a(); # OUTPUT: «called␤» 

(Callable) method assuming

method assuming(Callable:D $self: |primers)

Returns a Callable that implements the same behaviour as the original, but has the values passed to .assuming already bound to the corresponding parameters.

my sub slow($n){ my $i = 0$i++ while $i < $n$i };
 
# takes only one parameter and as such wont forward $n 
sub bench(&c){ cnow - ENTER now };
 
say &slow.assuming(10000000).&bench# OUTPUT: «(10000000 7.5508834)␤» 

Routines supplied by class Any

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

(Any) method ACCEPTS

Defined as:

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

Usage:

EXPR.ACCEPTS(EXPR);

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:

method list(--> List:D)

Interprets the invocant as a list, and returns that 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;
dd %h<a>;      # Any (and therefore undefined) 
%h<a>.push(1); # .push on Any 
dd %h;         # «Hash %h = {:a($[1])}␤» # please note the Array 

(Any) routine reverse

Defined as:

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

Returns a Seq say reverse ^10; # OUTPUT: «(9 8 7 6 5 4 3 2 1 0)␤»

(Any) method sort

Sorts iterables with infix:<cmp> or given code object and returns a new List.

Examples:

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)
multi method map(HyperIterable:D: &block;; :$label)

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.

dd [[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.

my @a = [1,[2,3],4];
dd @a.duckmap({ $_ ~~ Int ?? $_++ !! Any });
# OUTPUT: «(1, (2, 3), 4)␤» 

(Any) method flat

Defined as:

method flat(--> Seq:Dis nodal

Interprets the invocant as a list, flattens it, and returns that list. Please note that .flat will not solve the halting problem for you. If you flat an infinite list .flat may return that infinite list, eating all your RAM in the process.

say ((12), (3)).elems;        # OUTPUT: «2␤» 
say ((12), (3)).flat.elems;   # OUTPUT: «3␤» 

Please note that flat does not recurse into sub lists. You have to recurse by hand or reconsider your data structures. A single level of nesting can often be handled with destructuring in signatures. For deeper structures you may consider gather/take to create a lazy list.

my @a = [[1,2,3],[[4,5],6,7]];
say gather deepmap *.take@a# OUTPUT: «(1 2 3 4 5 6 7)␤» 

(Any) method eager

Defined as:

method eager(--> Seq:Dis nodal

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

say (1..10).eager;              # OUTPUT: «(1 2 3 4 5 6 7 8 9 10)␤» 

(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 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.

(Any) sub item

Defined as:

proto sub item(|) is pure
multi sub item(\x)
multi sub item(|c)
multi sub 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.

(Any) method Hash

Defined as:

method Hash(--> Hash:Dis nodal

Coerce the invocant to Hash.

(Any) method hash

Defined as:

method hash(--> Hash:Dis nodal

Coerce the invocant to Hash.

(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 and then to a Supply.

(Any) method min

Defined As:

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

Coerces to Iterable and returns the numerically smallest element. If a Callable is provided it is called with each element and its smallest return values is returned.

(Any) method max

Defined As:

multi method max(--> Any:D)
multi method min(&by --> Any:D)

Coerces to Iterable and returns the numerically biggest element. If a Callable is provided it is called with each element and its biggest return values is returned.

(Any) method minmax

Defined As:

multi method minmax(--> List:D)
multi method minmax(&by --> List:D)

Returns a list containing the smallest and the biggest element. If a Callable is provided each element is filtered and then numerically compared.

TODO

(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 sum

Defined As:

    method sum(--> TODO)

TODO

(Any) method keys

Defined As:

    method keys(--> TODO)

TODO

(Any) method flatmap

Defined As:

    method flatmap(--> TODO)

TODO

(Any) method roll

Defined As:

    method roll(--> TODO)

TODO

(Any) method pick

Defined As:

    method pick(--> TODO)

TODO

(Any) method head

Defined As:

    method head(--> TODO)

TODO

(Any) method tail

Defined As:

    method tail(--> TODO)

TODO

(Any) method skip

Defined As:

    method skip(--> TODO)

TODO

(Any) method prepend

Defined As:

    method prepend(--> TODO)

TODO

(Any) method unshift

Defined As:

    method unshift(--> TODO)

TODO

(Any) method first

Defined As:

    method first(--> TODO)

TODO

(Any) method unique

Defined As:

    method unique(--> TODO)

TODO

(Any) method repeated

Defined As:

    method repeated(--> TODO)

TODO

(Any) method squish

Defined As:

    method squish(--> TODO)

TODO

(Any) method reduce

Defined As:

    method reduce(--> TODO)

TODO

(Any) method permutations

Defined As:

    method permutations(--> TODO)

TODO

(Any) method categorize

Defined As:

    method categorize(--> TODO)

TODO

(Any) method classify

Defined As:

    method classify(--> TODO)

TODO

(Any) method produce

Defined As:

    method produce(--> TODO)

TODO

(Any) method rotor

Defined As:

    method rotor(--> TODO)

TODO

(Any) method pairs

Defined As:

    method pairs(--> TODO)

TODO

(Any) method antipairs

Defined As:

    method antipairs(--> TODO)

TODO

(Any) method kv

Defined As:

    method kv(--> TODO)

TODO

(Any) method tree

Defined As:

    method tree(--> TODO)

TODO

(Any) method nl-out

Defined As:

    method nl-out(--> TODO)

TODO

(Any) method invert

Defined As:

    method invert(--> TODO)

TODO

(Any) method combinations

Defined As:

    method combinations(--> TODO)

TODO

(Any) method print-nl

Defined As:

    method print-nl(--> TODO)

TODO

(Any) method nodemap

Defined As:

    method nodemap(--> TODO)

TODO

(Any) method iterator

Defined As:

    method iterator(--> TODO)

TODO

(Any) method grep

Defined As:

    method grep(--> TODO)

TODO

(Any) method match

Defined As:

    method match(--> TODO)

TODO

(Any) method append

Defined As:

    method append(--> TODO)

TODO

(Any) method join

Defined As:

    method join(--> TODO)

TODO

(Any) method values

Defined As:

    method values(--> TODO)

TODO

(Any) method collate

Defined As:

    method collate(--> TODO)

TODO

(Any) method batch

Defined As:

    method batch(--> TODO)

TODO

(Any) method cache

Defined As:

    method cache(--> TODO)

TODO

Routines supplied by class Mu

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

(Mu) routine defined

multi sub    defined(Mu --> Bool:D)
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 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 = Date.new('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 = Date.new('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 Mu.new.Bool;                # 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 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(Mu --> 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 Mu.new.gist;    # OUTPUT: «Mu.new␤» 

(Mu) routine perl

multi sub    perl(Mu --> Str)
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. 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:{
        "Point($.x$.y)";
    }
}
 
my $p = Point2D.new(x => 2=> 3);
 
say $p;                     # OUTPUT: «Point(2, 3)␤» 
say $p.clone(=> -5);      # OUTPUT: «Point(2, -5)␤» 

(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$y{
        self.bless(:$x:$y);
    }
}
my $p = Point.new(-11);

(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()

Returns the attached Pod value. For instance,

sub cast(Spell $s)
#= Initiate a specified spell normally 
#= (do not use for class 7 spells) 
{
do-raw-magic($s);
}
say &cast.WHY;

prints

Initiate a specified spell normally (do not use for class 7 spells)

See the documentation specification 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 };
dd 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} ($_)";
}}
 
# OUTPUT: 
# 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 $verbose-selected.so {
    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␤»