class Set

Immutable collection of distinct objects

class Set does Setty { }

A Set is an immutable set, meaning a collection of distinct elements in no particular order. (For mutable sets, see SetHash instead.)

Objects/values of any type are allowed as set elements. Within a Set, every element is guaranteed to be unique (in the sense that no two elements would compare positively with the === operator):

my $fruits = set <peach apple orange apple apple>;
say $fruits.elems;      # OUTPUT: «3␤» 
say $fruits.keys.sort;  # OUTPUT: «apple orange peach␤» 

Sets can be treated as object hashes using the { } postcircumfix operator, which returns the value True for keys that are elements of the set, and False for keys that aren't:

my $fruits = set <peach apple orange apple apple>;
say $fruits<apple>;  # OUTPUT: «True␤» 
say $fruits<kiwi>;   # OUTPUT: «False␤»

Creating Set objects

Sets can be composed using the set subroutine (or, for which it is a shorthand). Any positional parameters, regardless of their type, become elements of the set:

my $n = set "zero" => 0"one" => 1"two" => 2;
say $n.keys.perl;        # OUTPUT: «(:two(2), :zero(0), :one(1)).Seq␤» 
say $;  # OUTPUT: «((Pair) (Pair) (Pair))␤»

Alternatively, the .Set coercer (or its functional form, Set()) can be called on an existing object to coerce it to a Set. Its semantics depend on the type and contents of the object. In general it evaluates the object in list context and creates a set with the resulting items as elements, although for Hash-like objects or Pair items, only the keys become elements of the set - and keys mapped to values which boolify to False are skipped:

my $n = ("zero" => 0"one" => 1"two" => 2).Set;
say $n.keys.perl;        # OUTPUT: «("one", "two").Seq␤» 
say $;  # OUTPUT: «((Str) (Str))␤»

Furthermore, you can get a Set by using set operators (see next section) on objects of other types such as List, which will act like they internally call .Set on them before performing the operation. Be aware of the tight precedence of those operators though, which may require you to use parentheses around arguments:

say (1..5(^) 4;  # OUTPUT: «set(1, 2, 3, 5)␤»

Of course, you can also create a Set with the .new method.

my $fruits = <peach apple orange apple apple> );

Since 6.d (2019.03 and later) you can also use this syntax for parameterization of the Set, to specify which type of values are acceptable:

# only allow strings (Str) in the Set 
my $fruits = Set[Str].new( <peach apple orange apple apple> );
# only allow whole numbers (Int) in the Set 
my $fruits = Set[Int].new( <peach apple orange apple apple> );
# Type check failed in binding; expected Int but got Str ("peach")

Finally, you can create Set masquerading as a hash by using the is trait:

my %s is Set = <a b c>;
say %s<a>;  # True 
say %s<d>;  # False

Since 6.d (2019.03 and later), this syntax also allows you to specify the type of values you would like to allow:

# limit to strings 
my %s is Set[Str= <a b c>;
say %s<a>;  # True 
say %s<d>;  # False 
# limit to whole numbers 
my %s is Set[Int= <a b c>;
# Type check failed in binding; expected Int but got Str ("a")


Perl 6 provides common set operators, which can take Sets (or any other collections) as input, and return result sets as new Set objects. For example:

my ($a$b= set(123), set(24);
say $a (<) $b;  # OUTPUT: «False␤» 
say $a (&) $b;  # OUTPUT: «set(2)␤» 
say $a (^) $b;  # OUTPUT: «set(1, 3, 4)␤» 
# Unicode versions: 
say $a  $b;  # OUTPUT: «False␤» 
say $a  $b;  # OUTPUT: «set(2)␤» 
say $a  $b;  # OUTPUT: «set(1, 3, 4)␤» 

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


sub set

sub set(*@args --> Set)

Creates a Set from the given @args

See Also

Sets, Bags, and Mixes

Type Graph

Type relations for Set
perl6-type-graph Set Set Any Any Set->Any Setty Setty Set->Setty Mu Mu Any->Mu Associative Associative QuantHash QuantHash QuantHash->Associative Setty->QuantHash

Expand above chart

Routines supplied by role Setty

Set does role Setty, which provides the following routines:

(Setty) method new-from-pairs

Defined as:

method new-from-pairs(*@pairs --> Setty:D)

Constructs a Setty object from a list of Pair objects given as positional arguments:

say 'butter' => 0.22'salt' => 0'sugar' => 0.02;
# OUTPUT: «set(butter, sugar)␤»

Note: be sure you aren't accidentally passing the Pairs as positional arguments; the quotes around the keys in the above example are significant.

(Setty) method grab

method grab($count = 1)

Removes and returns $count elements chosen at random (without repetition) from the set.

If * is passed as $count, or $count is greater than or equal to the size of the set, then all its elements are removed and returned in random order.

Only works on mutable sets; When used on an immutable set, it results in an exception.

(Setty) method grabpairs

method grabpairs($count = 1)

Removes $count elements chosen at random (without repetition) from the set, and returns a list of Pair objects whose keys are the grabbed elements and whose values are True.

If * is passed as $count, or $count is greater than or equal to the size of the set, then all its elements are removed and returned as Pairs in the aforementioned way in random order.

Only works on mutable sets; When used on an immutable set, it results in an exception.

(Setty) method pick

multi method pick($count = 1)

Returns $count elements chosen at random (without repetition) from the set.

If * is passed as $count, or $count is greater than or equal to the size of the set, then all its elements are returned in random order (shuffled).

(Setty) method pickpairs

Defined as:

multi method pickpairs(Setty:D: --> Pair:D)
multi method pickpairs(Setty:D: $count --> Seq:D)

Returns a Pair or a Seq of Pairs depending on the candidate of the method being invoked. Each Pair returned has an element of the invocant as its key and True as its value. In contrast to grabpairs, the elements are 'picked' without replacement.

If * is passed as $count, or $count is greater than or equal to the number of elements of the invocant, then all element/True Pairs from the invocant are returned in a random sequence; i.e. they are returned shuffled;

Note that each pickpairs invocation maintains its own private state and has no effect on subsequent pickpairs invocations.

my $numbers = set (423);
say $numbers.pickpairs;                           # OUTPUT: «4 => True␤» 
say $numbers.pickpairs(1);                        # OUTPUT: «(3 => True)␤» 
say $numbers.pickpairs(*);                        # OUTPUT: «(2 => True 4 => True 3 => True)␤»

(Setty) method roll

multi method roll($count = 1)

Returns a lazy list of $count elements, each randomly selected from the set. Each random choice is made independently, like a separate die roll where each die face is a set element.

If * is passed as $count, the list is infinite.

(Setty) method antipairs

Defined as:

multi method antipairs(Setty:D: --> Seq:D)

Returns all elements in the set and True as a Seq of Pairs, where the element itself is the value, i.e. the opposite of method pairs.

my $s =;
say $s.antipairs.sort;                            # OUTPUT: «(True => 1 True => 2 True => 3)␤»

(Setty) method keys

Defined as:

multi method keys(Setty:D: --> Seq:D)

Returns a Seq of all elements of the set.

my $s =;
say $s.keys;                                      # OUTPUT: «(3 1 2)␤»

(Setty) method values

Defined as:

multi method values(Setty:D: --> Seq:D)

Returns a Seq containing as many True values as the set has elements.

my $s =;
say $s.values;                                    # OUTPUT: «(True True True)␤»

(Setty) method kv

Defined as:

multi method kv(Setty:D: --> Seq:D)

Returns a Seq of the set's elements and True values interleaved.

my $s =;
say $s.kv;                                        # OUTPUT: «(3 True 1 True 2 True)␤»

(Setty) method elems

method elems(--> Int)

The number of elements of the set.

(Setty) method total

method total(--> Int)

The total of all the values of the QuantHash object. For a Setty object, this is just the number of elements.

(Setty) method minpairs

Defined As:

multi method minpairs(Setty:D: --> Seq:D)

Returns the value of self.pairs (as all Pairs have minimum values). See also Any.minpairs

(Setty) method maxpairs

Defined As:

multi method maxpairs(Setty:D: --> Seq:D)

Returns the value of self.pairs (as all Pairs have maximum values). See also Any.maxpairs

(Setty) method default

Defined as:

method default(--> False)

Returns the default value of the invocant, i.e. the value which is returned when trying to access an element in the Setty object which has not been previously initialized or when accessing an element which has explicitly been set to Nil or False.

my $s1 =;
say $s1{2};                                           # OUTPUT: «True␤» 
$s1{2} = Nil;
say $s1{2};                                           # OUTPUT: «False␤» 
# access non initialized element 
say $s1{4};                                           # OUTPUT: «False␤»

(Setty) method ACCEPTS

method ACCEPTS($other)

Returns True if $other and self contain all the same elements, and no others.

(Setty) method Bag

Defined as:

method Bag(Setty:D: --> Bag:D)

Returns a Bag containing the elements of the invocant.

my Bag $b =;
say $b;                                           # OUTPUT: «bag(3, 1, 2)␤»

(Setty) method BagHash

Defined as:

method BagHash(Setty:D: --> BagHash:D)

Returns a BagHash containing the elements of the invocant.

my BagHash $b =;
say $b;                                           # OUTPUT: «, 1, 2)␤»

(Setty) method Bool

Defined as:

multi method Bool(Setty:D: --> Bool:D)

Returns True if the invocant contains at least one element.

my $s1 =;
say $s1.Bool;                                     # OUTPUT: «True␤» 
my $s2 = $s1;                     # set intersection operator 
say $s2.Bool;                                     # OUTPUT: «False␤»

(Setty) method Mix

Defined as:

method Mix(Setty:D: --> Mix:D)

Returns a Mix containing the elements of the invocant.

my Mix $b =;
say $b;                                           # OUTPUT: «mix(3, 1, 2)␤»

(Setty) method MixHash

Defined as:

method MixHash(Setty:D: --> MixHash:D)

Returns a MixHash containing the elements of the invocant.

my MixHash $b =;
say $b;                                           # OUTPUT: «, 1, 2)␤»

Routines supplied by role QuantHash

Set does role QuantHash, which provides the following routines:

(QuantHash) method hash

method hash()

Coerces the QuantHash object to a Hash (by stringifying the objects for the keys) with the values of the hash limited to the same limitation as QuantHash, and returns that.

(QuantHash) method Hash

method Hash()

Coerces the QuantHash object to a Hash (by stringifying the objects for the keys) without any limitations on the values, and returns that.

(QuantHash) method of

method of()

Returns the type of value a value of this QuantHash may have. This is typically Bool for Setty, UInt for Baggy or Real for Mixy roles.

(QuantHash) method keyof

method keyof()

Returns the type of value a key of this QuantHash may have. This is typically Mu.

(QuantHash) method Setty

method Setty(--> Setty:D)

Coerce the QuantHash object to the equivalent object that uses the Setty role. Note that for Mixy type coercion items with negative values will be skipped.

my %b is Bag = one => 1two => 2;
say %b.Setty# OUTPUT: «set(one two)␤» 
my %m is Mix = one => 1minus => -1;
say %m.Setty# OUTPUT: «set(one)␤»

(QuantHash) method Baggy

method Baggy(--> Baggy:D)

Coerce the QuantHash object to the equivalent object that uses the Baggy role. Note that for Mixy type coercion items with negative values will be skipped.

my %s is Set = <one two>;
say %s.Baggy# OUTPUT: «Bag(one, two)␤» 
my %m is Mix = one => 1minus => -1;
say %m.Baggy# OUTPUT: «Bag(one)␤»

(QuantHash) method Mixy

method Mixy(--> Mixy:D)

Coerce the QuantHash object to the equivalent object that uses the Mixy role.

my %s is Set = <one two>;
say %s.Mixy# OUTPUT: «Mix(one, two)␤» 
my %b is Bag = one => 1two => 2;
say %b.Mixy# OUTPUT: «Mix(one, two)␤»

Routines supplied by role Associative

Set does role Associative, which provides the following routines:

(Associative) method of

Defined as:

method of()

Associative is actually a parameterized role which can use different classes for keys and values. As seen at the top of the document, by default it coerces to Str for the key and uses a very generic Mu for value.

my %any-hash;
say %any-hash.of;#  OUTPUT: «(Mu)␤»

The value is the first parameter you use when instantiating Associative with particular classes:

class DateHash is Hash does Associative[Cool,DateTime{};
my %date-hash :=;
say %date-hash.of# OUTPUT: «(Cool)␤»

(Associative) method keyof

Defined as:

method keyof()

Returns the parameterized key used for the Associative role, which is Any coerced to Str by default. This is the class used as second parameter when you use the parameterized version of Associative.

my %any-hash;
%any-hash.keyof#OUTPUT: «(Str(Any))␤»

(Associative) method AT-KEY

method AT-KEY(\key)

Should return the value / container at the given key.

(Associative) method EXISTS-KEY

method EXISTS-KEY(\key)

Should return a Bool indicating whether the given key actually has a value.

(Associative) method STORE

method STORE(\values:$initialize)

This method should only be supplied if you want to support the:

my %h is Foo = => 42=> 666;

syntax for binding your implementation of the Associative role.

Should accept the values to (re-)initialize the object with, which either could consist of Pairs, or separate key/value pairs. The optional named parameter will contain a True value when the method is called on the object for the first time. Should return the invocant.