ImmSet

:::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. :::

ImmSet is an immutable, 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.

An ImmSet cannot be mutated. No elements can be added or removed from it, nor can elements be overwritten using assignment (i.e. $s[$k] = $v is not allowed).

Construct it with a Traversable:

$a = vec[1, 2];
$s = new ImmSet($a);

or use the literal syntax:

$s = ImmSet {1, 2};

Guides

• Introduction
• Classes

Interface Synopsis

namespace HH;

final class ImmSet implements \ConstSet<Tv> {...}

Public Methods

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