T M
class SetHash
Error ReportCollection examples

Mutable collection of distinct objects

class SetHash does Setty { }

A SetHash is a mutable set, meaning a collection of distinct elements in no particular order. (For immutable sets, see Set 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 = <peach apple orange apple apple>.SetHash;
 
say $fruits.elems;      # OUTPUT: «3␤» 
say $fruits.keys.sort;  # OUTPUT: «apple orange peach␤» 

Just like Sets, SetHashes 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 = <peach apple orange apple apple>.SetHash;
 
say $fruits<apple>;     # OUTPUT: «True␤» 
say $fruits<kiwi>;      # OUTPUT: «False␤» 

Unlike Sets, SetHashes are mutable. You can add an item or list of items to the SetHash with the set method and can remove an item or list of items with the unset method:

my $fruits = <peach>.SetHash;
$fruits.set('apple');
say $fruits;            # OUTPUT: «SetHash(apple peach)␤» 
 
$fruits.unset('peach');
say $fruits;            # OUTPUT: «SetHash(apple)␤» 
 
$fruits.set(<kiwi banana apple>);
say $fruits;            # OUTPUT: «SetHash(apple banana kiwi)␤» 
 
$fruits.unset(<apple banana kiwi>);
say $fruits;            # OUTPUT: «SetHash()␤» 

Be careful not to confuse the set method, which adds an item to a SetHash with the Set method, which converts the mutable SetHash into an immutable Set.

As an alternative to using the set and unset methods, you can also add or remove set elements by assigning a value that boolifies to True or False, respectively:

my $fruits = <peach apple orange>.SetHash;
 
$fruits<apple kiwi> = FalseTrue;
say $fruits.keys.sort;  # OUTPUT: «kiwi orange peach␤» 

Here is a convenient shorthand idiom for adding and removing SetHash elements using assignment:

my SetHash $fruits .= new;
say $fruits<cherry>;      # OUTPUT: «False␤» 
$fruits<cherry>++;
say $fruits<cherry>;      # OUTPUT: «True␤» 
$fruits<apple banana kiwi>»++# Add multiple elements 
 
$fruits<cherry>--;
say $fruits<cherry>;      # OUTPUT: «False␤» 
$fruits<banana kiwi>»--# Remove multiple elements 
 

Creating SetHash objects

SetHashes can be composed using SetHash.new. Any positional parameters, regardless of their type, become elements of the set:

my $n = SetHash.new: "zero" => 0"one" => 1"two" => 2;
say $n.keys.raku;        # OUTPUT: «(:two(2), :zero(0), :one(1)).Seq␤» 
say $n.keys.map(&WHAT);  # OUTPUT: «((Pair) (Pair) (Pair))␤»

Alternatively, the .SetHash coercer (or its functional form, SetHash()) can be called on an existing object to coerce it to a SetHash. 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).SetHash;
say $n.keys.raku;        # OUTPUT: «("one", "two").Seq␤» 
say $n.keys.map(&WHAT);  # OUTPUT: «((Str) (Str))␤»

It is also possible to initialize a single key with the use of {}:

my $sh = SetHash.new;
$sh{ 'key1' } = True;
$sh{ 'key2' } = 'Hello World!';
$sh{ 'key3' } = 0;  # does not store the key since 0.Bool is False 
say $sh;            # OUTPUT: «SetHash(key1 key2)␤» 
say $sh.keys.raku;  # OUTPUT: «("key1", "key2").Seq␤»

or, in order to initialize more than one key at the same time, use a list assignment:

my $sh = SetHash.new;
$sh{ 'a''b''c' } = TrueFalseTrue;
say $sh.keys.raku;  # OUTPUT: «("a", "c").Seq␤»

You can also create SetHash masquerading as a hash by using the is trait:

my %sh is SetHash = <a b c>;
say %sh<a>;  # True 
say %sh<d>;  # False

Since 6.d (2019.03 and later) it is also possible to specify the type of values you would like to allow in a SetHash. This can either be done when calling .new:

# only allow Pairs 
my $n = SetHash[Pair].new: "zero" => 0"one" => 1"two" => 2;

or using the masquerading syntax:

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

Operators

See Operators with set semantics for a complete list of "set operators" applicable to, among other types, SetHash.

Examples:

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

Methods

method set

Defined as:

method set(SetHash:D: \to-set --> Nil)

When given single key, set adds it to the SetHash. When given a List, Array, Seq, or any other type that does the Iterator Role, set adds each element of the Iterator as key to the SetHash.

Note: since version 2020.02.

method unset

Defined as:

method unset(SetHash:D: \to-unset --> Nil)

When given single key, unset removes it from the SetHash. When given a List, Array, Seq, or any other type that does the Iterator Role, unset removes each element of the Iterator from the SetHash (if it was present as a key).

Note: since version 2020.02.

See Also

Sets, Bags, and Mixes