class Whatever

Placeholder for unspecified value/parameter

class Whatever { }

Whatever is a class whose objects don't really do much; it gets its semantic from other routines that accept Whatever-objects as markers to do something special. The * literal in term position creates a Whatever object.

Another source of speciality is that the compiler turns combinations of * in term position and many operators into closures. This process is called Whatever-currying.

my $c = * + 2;          # same as   -> $x { $x + 2 };
say $c(4);              # 6

Multiple * in one expression generate closures with as many arguments:

my $c = * + *;          # same as   -> $x, $y { $x + $y }

* in complex expressions also generate closures:

my $c = 4 * * + 5;      # same as   -> $x { 4 * $x + 5 }

Calling a method on * also create a closure:

say <a b c>.map: *.uc;  # A B C

Those closure are of type WhateverCode.

Not all operators and syntactic constructs curry Whatever-stars.

Exception Example What it does
comma 1, *, 2 generates a Parcel with a * element
range operators 1..* Range.new(:from(1), :to(*));
series operator 1 ... * infinite list
smart-matching 1 ~~ * returns True
assignment $x = * assign * to $x
binding $x := * binds * to $x
list repetition 1 xx * generates infinite list

The range operators are handled specially. They do not curry with Whatever-stars, but they do curry with WhateverCode

say (1..*).WHAT;        # Range
say (1..*-1).WHAT;      # WhateverCode

This allow all these constructs to work:

.say for 1..*;          # infinite loop
my @a = 1..4;
say @a[1..*];           # 2 3 4
say @a[1..*-2];         # 2 3

The currying is purely syntactic.

my $x = *;
$x + 2;                 # not a closure, dies because
                        # it can't coerce $x to Numeric

Methods

method ACCEPTS

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

Returns True.

Type graph

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

perl6-type-graph Whatever Whatever Any Any Whatever->Any Mu Mu Any->Mu

Methods supplied by class Any

Whatever 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

Whatever 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.