Set

:::info[Note] This is a point-in-time snapshot of the API documentation from January 2026. Going forward, we will not be maintaining a public copy of these references, and recommend users to refer to the built-in signature helpers available in the Hack LSP instead for complete and up-to-date information. :::

Set is an ordered set-style collection

HHVM provides a native implementation for this class. The PHP class definition below is not actually used at run time; it is simply provided for the typechecker and for developer reference.

Like all objects in PHP, Sets have reference-like semantics. When a caller passes a Set to a callee, the callee can modify the Set and the caller will see the changes. Sets do not have "copy-on-write" semantics.

Sets preserve insertion order of the elements. When iterating over a Set, the elements appear in the order they were inserted. Also, Sets do not automagically convert integer-like strings (ex. "123") into integers.

Sets only support int values and string values. If a value of a different type is used, an exception will be thrown.

In general, Sets do not support $c[$k] style syntax. Adding an element using $c[] = .. syntax is supported.

Set do not support iteration while elements are being added or removed. When an element is added or removed, all iterators that point to the Set shall be considered invalid.

Guides

• Introduction
• Classes

Examples

More documentation and examples are in the Set and ImmSet guide.

Interface Synopsis

namespace HH;

final class Set implements \MutableSet<Tv> {...}

Public Methods

• ::fromArray(darray<arraykey, Tv> $arr): Set<Tv>
  Returns a Set containing the values from the specified array
• ::fromArrays(...$argv): Set<Tv>
  Returns a Set containing all the values from the specified array(s)
• ::fromItems(?Traversable<Tv> $iterable): Set<Tv>
  Creates a Set from the given Traversable, or an empty Set if null is passed
• ::fromKeysOf<Tk as arraykey>(?KeyedContainer<Tk, mixed> $container): Set<Tk>
  Creates a Set from the keys of the specified container
• ->__construct(?Traversable<Tv> $iterable = NULL): void
  Creates a Set from the given Traversable, or an empty Set if null is passed
• ->__toString(): string
  Returns the string version of the current Set, which is "Set"
• ->add(Tv $val): Set<Tv>
  Add the value to the current Set
• ->addAll(?Traversable<Tv> $iterable): Set<Tv>
  For every element in the provided Traversable, add the value into the current Set
• ->addAllKeysOf(?KeyedContainer<Tv, mixed> $container): Set<Tv>
  Adds the keys of the specified container to the current Set as new values
• ->clear(): Set<Tv>
  Remove all the elements from the current Set
• ->concat<Tu super Tv>(Traversable<Tu> $traversable): Vector<Tu>
  Returns a Vector that is the concatenation of the values of the current Set and the values of the provided Traversable
• ->contains(arraykey $val): bool
  Determines if the specified value is in the current Set
• ->count(): int
  Provides the number of elements in the current Set
• ->difference(mixed $iterable)
• ->filter((function(Tv): bool) $callback): Set<Tv>
  Returns a Set containing the values of the current Set that meet a supplied condition applied to each value
• ->filterWithKey((function(arraykey, Tv): bool) $callback): Set<Tv>
  Returns a Set containing the values of the current Set that meet a supplied condition applied to its "keys" and values
• ->firstKey(): ?arraykey
  Returns the first "key" in the current Set
• ->firstValue(): ?Tv
  Returns the first value in the current Set
• ->getIterator(): KeyedIterator<arraykey, Tv>
  Returns an iterator that points to beginning of the current Set
• ->immutable(): ImmSet<Tv>
  Returns an immutable (ImmSet), deep copy of the current Set
• ->isEmpty(): bool
  Checks if the current Set is empty
• ->items(): Iterable<Tv>
  Returns an Iterable view of the current Set
• ->keys(): Vector<arraykey>
  Returns a Vector containing the values of the current Set
• ->lastKey(): ?arraykey
  Returns the last "key" in the current Set
• ->lastValue(): ?Tv
  Returns the last value in the current Set
• ->lazy(): KeyedIterable<arraykey, Tv>
  Returns a lazy, access elements only when needed view of the current Set
• ->map<Tu as arraykey>((function(Tv): Tu) $callback): Set<Tu>
  Returns a Set containing the values after an operation has been applied to each value in the current Set
• ->mapWithKey<Tu as arraykey>((function(arraykey, Tv): Tu) $callback): Set<Tu>
  Returns a Set containing the values after an operation has been applied to each "key" and value in the current Set
• ->remove(Tv $val): Set<Tv>
  Removes the specified value from the current Set
• ->removeAll(Traversable<Tv> $iterable): Set<Tv>
  Removes the values in the current Set that are also in the Traversable
• ->reserve(int $sz): void
  Reserves enough memory to accommodate a given number of elements
• ->retain((function(Tv): bool) $callback): Set<Tv>
  Alters the current Set so that it only contains the values that meet a supplied condition on each value
• ->retainWithKey((function(arraykey, Tv): bool) $callback): Set<Tv>
  Alters the current Set so that it only contains the values that meet a supplied condition on its "keys" and values
• ->skip(int $n): Set<Tv>
  Returns a Set containing the values after the n-th element of the current Set
• ->skipWhile((function(Tv): bool) $fn): Set<Tv>
  Returns a Set containing the values of the current Set starting after and including the first value that produces true when passed to the specified callback
• ->slice(int $start, int $len): Set<Tv>
  Returns a subset of the current Set starting from a given key up to, but not including, the element at the provided length from the starting key
• ->take(int $n): Set<Tv>
  Returns a Set containing the first n values of the current Set
• ->takeWhile((function(Tv): bool) $callback): Set<Tv>
  Returns a Set containing the values of the current Set up to but not including the first value that produces false when passed to the specified callback
• ->toDArray(): darray<Tv, Tv>
  Returns a darray built from the values from this Set, darray[val1 => val1, val2 => val2, ...]
• ->toImmMap(): ImmMap<arraykey, Tv>
  Returns an immutable map (ImmMap) based on the values of the current Set
• ->toImmSet(): ImmSet<Tv>
  Returns an immutable (ImmSet), deep copy of the current Set
• ->toImmVector(): ImmVector<Tv>
  Returns an immutable vector (ImmVector) with the values of the current Set
• ->toKeysArray(): varray<Tv>
  Returns an array containing the values from the current Set
• ->toMap(): Map<arraykey, Tv>
  Returns a Map based on the values of the current Set
• ->toSet(): Set<Tv>
  Returns a deep copy of the current Set
• ->toVArray(): varray<Tv>
• ->toValuesArray(): varray<Tv>
  Returns an array containing the values from the current Set
• ->toVector(): Vector<Tv>
  Returns a Vector of the current Set values
• ->values(): Vector<Tv>
  Returns a Vector containing the values of the current Set
• ->zip<Tu>(Traversable<Tu> $traversable): Set<nothing>
  Throws an exception unless the current Set or the Traversable is empty