ImmMap

:::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. :::

ImmMap is an immutable Map

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.

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

Construct it with a Traversable:

$a = dict['a' => 1, 'b' => 2];
$fm = new ImmMap($a);

or use the literal syntax

$fm = ImmMap {'a' => 1, 'b' => 2};

Guides

• Introduction
• Classes

Interface Synopsis

namespace HH;

final class ImmMap implements \ConstMap<Tk, Tv> {...}

Public Methods

• ::fromItems(?Traversable<Pair<Tk, Tv>> $iterable): ImmMap<Tk, Tv>
  Creates an ImmMap from the given Traversable, or an empty ImmMap if null is passed
• ->__construct(?KeyedTraversable<Tk, Tv> $iterable = NULL): void
  Creates an ImmMap from the given KeyedTraversable, or an empty ImmMap if null is passed
• ->__toString(): string
  Returns the string version of the current ImmMap, which is "ImmMap"
• ->at(Tk $key): Tv
  Returns the value at the specified key in the current ImmMap
• ->concat<Tu super Tv>(Traversable<Tu> $traversable): ImmVector<Tu>
  Returns an ImmVector that is the concatenation of the values of the current ImmMap and the values of the provided Traversable
• ->contains(mixed $key): bool
  Determines if the specified key is in the current ImmMap
• ->containsKey(mixed $key): bool
  Determines if the specified key is in the current ImmMap
• ->count(): int
  Provides the number of elements in the current ImmMap
• ->differenceByKey(KeyedTraversable<mixed, mixed> $traversable): ImmMap<Tk, Tv>
  Returns a new ImmMap with the keys that are in the current ImmMap, but not in the provided KeyedTraversable
• ->filter((function(Tv): bool) $callback): ImmMap<Tk, Tv>
  Returns an ImmMap containing the values of the current ImmMap that meet a supplied condition
• ->filterWithKey((function(Tk, Tv): bool) $callback): ImmMap<Tk, Tv>
  Returns an ImmMap containing the values of the current ImmMap that meet a supplied condition applied to its keys and values
• ->firstKey(): ?Tk
  Returns the first key in the current ImmMap
• ->firstValue(): ?Tv
  Returns the first value in the current ImmMap
• ->get(Tk $key): ?Tv
  Returns the value at the specified key in the current ImmMap
• ->getIterator(): KeyedIterator<Tk, Tv>
  Returns an iterator that points to beginning of the current ImmMap
• ->immutable(): ImmMap<Tk, Tv>
  Returns an immutable copy (ImmMap) of the current ImmMap
• ->isEmpty(): bool
  Checks if the current ImmMap is empty
• ->items(): Iterable<Pair<Tk, Tv>>
  Returns an Iterable view of the current ImmMap
• ->keys(): ImmVector<Tk>
  Returns an ImmVector containing, as values, the keys of the current ImmMap
• ->lastKey(): ?Tk
  Returns the last key in the current ImmMap
• ->lastValue(): ?Tv
  Returns the last value in the current ImmMap
• ->lazy(): KeyedIterable<Tk, Tv>
  Returns a lazy, access elements only when needed view of the current ImmMap
• ->map<Tu>((function(Tv): Tu) $callback): ImmMap<Tk, Tu>
  Returns an ImmMap after an operation has been applied to each value in the current ImmMap
• ->mapWithKey<Tu>((function(Tk, Tv): Tu) $callback): ImmMap<Tk, Tu>
  Returns an ImmMap after an operation has been applied to each key and value in current ImmMap
• ->skip(int $n): ImmMap<Tk, Tv>
  Returns an ImmMap containing the values after the n-th element of the current ImmMap
• ->skipWhile((function(Tv): bool) $fn): ImmMap<Tk, Tv>
  Returns an ImmMap containing the values of the current ImmMap starting after and including the first value that produces true when passed to the specified callback
• ->slice(int $start, int $len): ImmMap<Tk, Tv>
  Returns a subset of the current ImmMap starting from a given key location up to, but not including, the element at the provided length from the starting key location
• ->take(int $n): ImmMap<Tk, Tv>
  Returns an ImmMap containing the first n key/values of the current ImmMap
• ->takeWhile((function(Tv): bool) $callback): ImmMap<Tk, Tv>
  Returns an ImmMap containing the keys and values of the current ImmMap up to but not including the first value that produces false when passed to the specified callback
• ->toDArray(): darray<Tk, Tv>
  Returns a darray built from the keys and values from this ImmMap
• ->toImmMap(): ImmMap<Tk, Tv>
  Returns an immutable copy (ImmMap) of the current ImmMap
• ->toImmSet(): ImmSet<Tv>
  Returns an immutable set (ImmSet) based on the values of the current ImmMap
• ->toImmVector(): ImmVector<Tv>
  Returns an immutable vector (ImmVector) with the values of the current ImmMap
• ->toKeysArray(): varray<Tk>
  Returns an array whose values are the keys of the current ImmMap
• ->toMap(): object
  Returns a Map built from the keys and values of this ImmMap
• ->toSet(): object
  Returns a Set built from the values of this ImmMap
• ->toVArray(): varray<Tv>
• ->toValuesArray(): varray<Tv>
  Returns an array containing the values from the current ImmMap
• ->toVector(): object
  Returns a Vector built from the values of this ImmMap
• ->values(): ImmVector<Tv>
  Returns an ImmVector containing the values of the current ImmMap
• ->zip<Tu>(Traversable<Tu> $traversable): ImmMap<Tk, Pair<Tv, Tu>>
  Returns an ImmMap where each value is a Pair that combines the value of the current ImmMap and the provided Traversable