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Programming-Idioms

  • Java
  • Pascal
  • Go

Idiom #34 Create a set of objects

Declare and initialize a set x containing unique objects of type T.

x := make(map[T]bool)

There is no built-in Set type, but you can create a Map with key type T and boolean value (which will be ignored).
x := make(map[T]struct{})

The struct{} type is space efficient because it occupies zero bytes in memory.
import static java.util.Set.of;
import java.util.Set;
Set<T> x = of(a, b, c);
import java.util.Set;
import java.util.HashSet;
Set<T> x = new HashSet<T>();
x.add(a);
x.add(b);

T should override equals(), per the Set contract.
T should override hashCode(), per the HashSet contract.
import java.util.Set;
import java.util.HashSet;
Set<T> x = new HashSet<T>();

The type T must respect the equals() / hashcode() contract.
#include <unordered_set>
std::unordered_set<T, hasher, eq> x;

Using a custom hasher and eq (equality checking function)
New implementation...
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programming-idioms.org 
x := make(map[T]bool)
x := make(map[T]struct{})
Set<T> x = of(a, b, c);
Set<T> x = new HashSet<T>();
x.add(a);
x.add(b);
Set<T> x = new HashSet<T>();
std::unordered_set<T, hasher, eq> x;
std::unordered_set<T> x;
HashSet<T> x = new HashSet<T>();
auto x = redBlackTree!T;
var x = new Set<T>();
x = empty :: Set T

let x = new Set();
class T {}
class Set::Object::T extends Set::Object {
    method BUILDARGS(T @items) { return {data => \@items}; }
    method insert(T @items) { $self->next::method(@items); }
}
my $x = Set::Object::T->new(T->new, T->new, T->new);
class T(object):
    pass

x = set(T())
class T:
   ...

s = set(T() for _ in range(x))
class T:
    def __init__(self, x):
        self.x = x
    def __hash__(self):
        return hash(self.x)
    def __eq__(self, t):
        return self.x == t.x
x = {T('abc'), T(123), T(lambda: ...)}
x = Set.new
let x: HashSet<T> = HashSet::new();
val x = Set[T]()