class Pair

class Pair is Enum { ... }

Consists of two parts, a key and a value. Pairs can be seen as the atomic units in Hashes, and they are also used in conjunction with named arguments and parameters.

: => :! There are three syntaxes for Pairs:

'key' => 'value'    # this...
:key<value>         # ...means the same as this
:$foo               # short for foo => $foo

Variants of this are

:key                # same as   key => True
:!key               # same as   key => False

The immutable version of a Pair is an Enum.

Methods

method value

multi method value(Pair:D:) is rw

Returns the value part of the Pair.

infix cmp

multi sub infix:<cmp>(Pair:D, Pair:D)

The type-agnostic comparator; compares two Pairs. Compares first their key parts, and then compares the value parts if the keys are equal.

method fmt

multi method fmt(Pair:D:) returns Str:D

Takes a format string, and returns a string the key and value parts of the Pair formatted. Here's an example:

my $pair = :Earth(1);
say $pair.fmt("%s is %.3f AU away from the sun")
# Prints "Earth is 1.000 AU away from the sun"

For more about format strings, see sprintf.

method kv

multi method kv(Pair:D:) returns Parcel:D

Returns a two-element Parcel with the key and value parts o Pair, in that order. This method is a special case of the same-named method on Hash, which returns all its entries as a list of keys and values.

method pairs

multi method pairs(Pair:D:)

Returns a list of one Pair, namely this one.

Type graph

Below you should see an imgage showing the type relations for Pair. If not, try the PNG version.

perl6-type-graph Pair Pair Enum Enum Pair->Enum Mu Mu Any Any Any->Mu Associative Associative Enum->Any Enum->Associative

Methods supplied by class Enum

Pair inherits from class Enum, which provides the following methods:

method key

multi method key(Enum:D:)

Returns the key part of the Enum.

method value

multi method value(Enum:D:)

Returns the value part of the Enum.

method invert

multi method invert(Enum:D:) returns Enum:D

Returns a new Enum with the original enum's value as the key, and the original enum's key as value.

Methods supplied by class Any

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

method ACCEPTS

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

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

method any

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

method all

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

method one

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

method none

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

Methods supplied by class Mu

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

method Str

multi method Str()   returns Str

Returns a string representation of the invocant, intended to be machine readable.

method clone

method clone(*%twiddles)

Creates a shallow clone of the invocant. If named arguments are passed to it, their values are used in every place where an attribute name matches the name of a named argument.

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.

method bless

method bless(*%attrinit) returns 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).

method CREATE

method CREATE() returns Mu:D

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

method print

multi method print() returns Bool:D

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

method say

multi method say() returns Bool:D

Prints value to $*OUT after stringification using .gist method with newline at end.

method ACCEPTS

multi method ACCEPTS(Mu:U: $other)

Performs a type check. Returns True if $other conforms to the invocant (which is always a type object or failure).

This is the method that is triggered on smart-matching against type objects, for example in if $var ~~ Int { ... }.

method WHICH

multi method WHICH() returns 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.