class Attribute

Member variable

class Attribute { }

In Perl 6 lingo, an attribute refers to a per-instance/object storage slot. An Attribute is used to talk about classes' and roles' attributes on the meta level.

Normal usage of attributes does not require the user to use class Attribute explicitly.

The usual way to obtain an object of type Attribute is by introspection:

class Useless {
    has @!things;
}
my $a = Useless.^attributes(:local)[0];
say $a.name;            # OUTPUT: «@!things␤» 
say $a.package;         # OUTPUT: «(Useless)␤» 
say $a.has_accessor;    # OUTPUT: «False␤» 
 
# modifying an attribute from the outside 
# this is usually not possible, but since Attribute 
# is at the level of the meta class, all is fair game 
my $instance = Useless.new;
$a.set_value($instance, [1, 2, 3]);
say $a.get_value($instance);        # OUTPUT: «[1 2 3]␤» 

Traits

Trait is default

An attribute that is assigned Nil will revert to its default value set with the trait is default.

class C {
    has $.a is default(42) is rw = 666
}
my $c = C.new;
say $c;
$c.a = Nil;
say $c;
# OUTPUT: «C.new(a => 666)␤C.new(a => 42)␤» 

Trait is required

The trait is required will mark the attribute as to be filled with a value when the object is instantiated. Failing to do so will result in a runtime error.

class C {
    has $.a is required
}
my $c = C.new;
CATCH{ default { say .^name, ': ', .Str } }
# OUTPUT: «X::Attribute::Required: The attribute '$!a' is required, but you did not provide a value for it.␤» 

trait is DEPRECATED

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

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

TODO: Add example when it's implemented in Rakudo.

Methods

method name

Defined as:

method name(Attribute:D: --> Str:D)

Returns the name of the attribute. Note that this is always the private name, so if an attribute is declared as has $.a, the name returned is $!a.

class Foo {
    has @!bar;
}
my $a = Foo.^attributes(:local)[0];
say $a.name;            # OUTPUT: «@!bar␤» 

method package

Defined as:

method package(Attribute:D: --> Mu:U)

Returns the package (class/grammar/role) to which this attribute belongs.

class Boo {
    has @!baz;
}
my $a = Boo.^attributes(:local)[0];
say $a.package;         # OUTPUT: «(Boo)␤» 

method has_accessor

Defined as:

method has_accessor(Attribute:D: --> Bool:D)

Returns True if the attribute has a public accessor method.

class Container {
    has $!private;
    has $.public;
}
my $private = Container.^attributes(:local)[0];
my $public = Container.^attributes(:local)[1];
say $private.has_accessor; # OUTPUT: «False␤» 
say $public.has_accessor;  # OUTPUT: «True␤» 

method readonly

Defined as:

method readonly(Attribute:D: --> Bool:D)

Returns True for readonly attributes, which is the default. Returns False for attributes marked as is rw.

class Library {
    has $.address; # Read-only value 
    has @.new-books is rw;
}
my $addr = Library.^attributes(:local)[0];
my $new-books = Library.^attributes(:local)[1];
say $addr.readonly;      # OUTPUT: «True␤» 
say $new-books.readonly; # OUTPUT: «False␤» 

method type

Defined as:

method type(Attribute:D: --> Mu)

Returns the type constraint of the attribute.

class TypeHouse {
    has Int @.array;
    has $!scalar;
    has @.mystery;
}
my @types = TypeHouse.^attributes(:local)[0..2];
for 0..2 { say @types[$_].type }
# OUTPUT: «(Positional[Int]) 
# (Mu) 
# (Positional)␤» 

method get_value

Defined as:

method get_value(Attribute:D: Mu $instance)

Returns the value stored in this attribute of object $instance.

class Violated {
    has $!private-thing = 5;
}
my $private = Violated.^attributes(:local)[0];
say $private.get_value(Violated.new); # OUTPUT: «5␤» 

Note that this method violates encapsulation of the object, and should be used with care. Here be dragons.

method set_value

Defined as:

method set_value(Attribute:D: Mu $instance, Mu \new_val)

Binds the value new_val to this attribute of object $instance.

class A {
    has $!a = 5;
    method speak() { say $!a; }
}
my $attr = A.^attributes(:local)[0];
my $a = A.new;
$a.speak; # OUTPUT: «5␤» 
$attr.set_value($a, 42);
$a.speak; # OUTPUT: «42␤» 

Note that this method violates encapsulation of the object, and should be used with care. Here be dragons.

trait is required

multi sub trait_mod:<is> (Attribute $attr, :$required!)

Marks an attribute as being required. If a value is not provided during object construction, an exception is thrown.

class Foo {
   has $.bar is required;
   has $.baz;
};
 
Foo.new(bar => 42); # works 
Foo.new(baz => 42);
CATCH { default { put .^name, ': ', .Str } };
# OUTPUT: «X::Attribute::Required: The attribute '$!bar' is required, but you did not provide a value for it.␤» 

is required doesn't just affect the default constructor, it checks for the attribute at a lower level, so it will work for custom constructors written using bless.

trait is rw

multi sub trait_mod:<is> (Attribute:D $attr, :$rw!)

Marks an attribute as read/write as opposed to the default readonly. The default accessor for the attribute will return a writable value.

class Boo {
   has $.bar is rw;
   has $.baz;
};
 
my $boo = Boo.new;
$boo.bar = 42; # works 
$boo.baz = 42;
CATCH { default { put .^name, ': ', .Str } };
# OUTPUT: «X::Assignment::RO: Cannot modify an immutable Any␤» 

Type graph

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

Stand-alone image: vector

Routines supplied by class Any

Attribute 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 == (1, 2, 3).one;      # OUTPUT: «True␤» 
say so 1 == (1, 2, 1).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 == (1, 2, 3).none;     # OUTPUT: «False␤» 
say so 4 == (1, 2, 3).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 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.

Examples:

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(&by)

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

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 --> List) is 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(&block) is 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 --> List) is 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 [[2, 3], [4, [5, 6]]]».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:D) is 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 ((1, 2), (3), %(:42a));      # OUTPUT: «((1 2) 3 {a => 42})␤» 
say ((1, 2), (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 [[1, 2, 3], [(4, 5), 6, 7]]      .flat; # OUTPUT: «([1 2 3] [(4 5) 6 7])␤» 
say [[1, 2, 3], [(4, 5), 6, 7]]».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:D) is 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:D) is 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:D) is 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:D) is 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 (a => 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:D) is nodal

Coerce the invocant to Array.

(Any) method List

Defined as:

method List(--> List:D) is nodal

Coerce the invocant to List.

(Any) method Hash

Defined as:

method Hash(--> Hash:D) is nodal

Coerce the invocant to Hash.

(Any) method hash

Defined as:

method hash(--> Hash:D) is nodal

Coerce the invocant to Hash.

(Any) method Slip

Defined as:

method Slip(--> Slip:D) is nodal

Coerce the invocant to Slip.

(Any) method Map

Defined as:

method Map(--> Map:D) is nodal

Coerce the invocant to Map.

(Any) method Bag

Defined as:

method Bag(--> Bag:D) is nodal

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

(Any) method BagHash

Defined as:

method BagHash(--> BagHash:D) is nodal

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

(Any) method Set

Defined as:

method Set(--> Set:D) is nodal

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

(Any) method SetHash

Defined as:

method SetHash(--> SetHash:D) is nodal

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

(Any) method Mix

Defined as:

method Mix(--> Mix:D) is nodal

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

(Any) method MixHash

Defined as:

method MixHash(--> MixHash:D) is nodal

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

(Any) method Supply

Defined as:

method Supply(--> Supply:D) is 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 positional argument 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 max(&by --> Any:D)

Coerces to Iterable and returns the numerically biggest element. If a Callable positional argument 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 positional argument is provided each element is filtered and then numerically compared.

(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

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

(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 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

Attribute 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 [1, 2, 3].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

Defined 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, for non-Str types, 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, y => 3);
 
say $p;                     # OUTPUT: «Point(2, 3)␤» 
say $p.clone(y => -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(-1, 1);

(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 .take, next;
        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(@args) eq '-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(@args) eq '-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(@args) eq '-v' | '-V';
if not $verbose-selected {
    say "Verbose option not present in arguments";
} # OUTPUT: «Verbose option not present in arguments␤»