class Mix

Immutable collection of distinct objects with Real weights

class Mix does Mixy { }

A Mix is an immutable mix, meaning a collection of distinct elements in no particular order that each have a real-number weight assigned to them. (For mutable mixes, see MixHash instead.)

Mixes are often used for performing weighted random selections - see .roll.

Objects/values of any type are allowed as mix elements. Within a Mix, items that would compare positively with the === operator are considered the same element, with a combined weight.

my $recipe = (butter => 0.22, sugar => 0.1,
              flour => 0.275, sugar => 0.02).Mix

say $recipe.elems;      # 3
say $recipe.keys.sort;  # butter flour sugar
say $recipe.pairs.sort; # "butter" => 0.22 "flour" => 0.275 "sugar" => 0.12
say $;      # 0.615

Mixes can be treated as object hashes using the { } postcircumfix operator, which returns the corresponding numeric weight for keys that are elements of the mix, and 0 for keys that aren't:

say $recipe<butter>;     # 0.22
say $recipe<sugar>;      # 0.12
say $recipe<chocolate>;  # 0

Creating Mix objects

Mixes can be composed using the mix subroutine (or, for which it is a shorthand). Any positional parameters, regardless of their type, become elements of the mix - with a weight of 1 for each time the parameter occurred:

my $n = mix "a", "a", "b" => 0, "c" => 3.14;
say $;  # (Str) (Pair) (Pair)
say $n.pairs;            # "a" => 2 ("b" => 0) => 1 ("c" => 3.14) => 1

Alternatively, the .Mix coercer (or its functional form, Mix()) can be called on an existing object to coerce it to a Mix. Its semantics depend on the type and contents of the object. In general it evaluates the object in list context and creates a mix with the resulting items as elements, although for Hash-like objects or Pair items, only the keys become elements of the mix, and the (cumulative) values become the associated numeric weights:

my $n = ("a", "a", "b" => 0, "c" => 3.14).Mix;
say $;  # (Str) (Str)
say $n.pairs;            # "a" => 2 "c" => 3.14


See setbagmix#Set/Bag Operators for a complete list of set and bag operators with detailed explanations.

sub mix

sub mix(*@args --> Mix)

Creates a new Mix from @args.

See Also

Sets, Bags, and Mixes

Type graph

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

perl6-type-graph Mix Mix Any Any Mix->Any Mixy Mixy Mix->Mixy Mu Mu Any->Mu Associative Associative QuantHash QuantHash QuantHash->Associative Baggy Baggy Baggy->QuantHash Mixy->Baggy

Methods supplied by role Mixy

Mix does role Mixy, which provides the following methods:

method total

method total(--> Real)

Returns the sum of all the weights

mix('a','b','c','a','a','d').total == 6; # True
{a => 5.6, b => 2.4} == 8; # True

method roll

method roll ($count = 1)

Similar to a Bag.roll, but with Real weights rather than integral ones.

Methods supplied by class Any

Mix 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

Mix 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 =, 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.