MutableSet

:::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. :::

Represents a write-enabled (mutable) set of values, not indexed by keys (i.e. a set)

Guides

• Introduction
• Interfaces

Interface Synopsis

interface MutableSet implements ConstSet<Tv>, HH\Collection<Tv>, SetAccess<Tv> {...}

Public Methods

• ->concat<Tu super Tv>(Traversable<Tu> $traversable): MutableVector<Tu>
  Returns a MutableVector that is the concatenation of the values of the current MutableSet and the values of the provided Traversable
• ->filter((function(Tv): bool) $fn): MutableSet<Tv>
  Returns a MutableSet containing the values of the current MutableSet that meet a supplied condition applied to each value
• ->filterWithKey((function(arraykey, Tv): bool) $fn): MutableSet<Tv>
  Returns a MutableSet containing the values of the current MutableSet that meet a supplied condition applied to its "keys" and values
• ->firstKey(): ?arraykey
  Returns the first "key" in the current MutableSet
• ->firstValue(): ?Tv
  Returns the first value in the current MutableSet
• ->keys(): MutableVector<arraykey>
  Returns a MutableVector containing the values of the current MutableSet
• ->lastKey(): ?arraykey
  Returns the last "key" in the current MutableSet
• ->lastValue(): ?Tv
  Returns the last value in the current MutableSet
• ->map<Tu as arraykey>((function(Tv): Tu) $fn): MutableSet<Tu>
  Returns a MutableSet containing the values after an operation has been applied to each value in the current MutableSet
• ->mapWithKey<Tu as arraykey>((function(arraykey, Tv): Tu) $fn): MutableSet<Tu>
  Returns a MutableSet containing the values after an operation has been applied to each "key" and value in the current Set
• ->skip(int $n): MutableSet<Tv>
  Returns a MutableSet containing the values after the n-th element of the current MutableSet
• ->skipWhile((function(Tv): bool) $fn): MutableSet<Tv>
  Returns a MutableSet containing the values of the current MutableSet starting after and including the first value that produces true when passed to the specified callback
• ->slice(int $start, int $len): MutableSet<Tv>
  Returns a subset of the current MutableSet starting from a given key up to, but not including, the element at the provided length from the starting key
• ->take(int $n): MutableSet<Tv>
  Returns a MutableSet containing the first n values of the current MutableSet
• ->takeWhile((function(Tv): bool) $fn): MutableSet<Tv>
  Returns a MutableSet containing the values of the current MutableSet up to but not including the first value that produces false when passed to the specified callback
• ->toDArray(): darray<Tv, Tv>
• ->toVArray(): varray<Tv>
• ->values(): MutableVector<Tv>
  Returns a MutableVector containing the values of the current MutableSet
• ->zip<Tu>(Traversable<Tu> $traversable): MutableSet<nothing>
  Returns a MutableSet where each value is a Pair that combines the value of the current MutableSet and the provided Traversable

Public Methods (ConstCollection)

• ->count(): int
  Get the number of items in the collection

• ->isEmpty(): bool
  Is the collection empty?

• ->items(): HH\Iterable<Te>
  Get access to the items in the collection

Public Methods (IPureStringishObject)

• ->__toString(): string

Public Methods (ConstSetAccess)

• ->contains(arraykey $m): bool
  Checks whether a value is in the current Set

Public Methods (HH\KeyedIterable)

• ->getIterator(): KeyedIterator<Tk, Tv>
  Returns an iterator that points to beginning of the current KeyedIterable
• ->lazy(): KeyedIterable<Tk, Tv>
  Returns a lazy, access elements only when needed view of the current KeyedIterable
• ->toImmMap(): ImmMap<Tk, Tv>
  Returns an immutable map (ImmMap) based on the keys and values of the current KeyedIterable
• ->toKeysArray(): varray
  Returns an array with the keys from the current KeyedIterable

Public Methods (HH\Iterable)

• ->toImmSet(): ImmSet<Tv>
  Returns an immutable set (ImmSet) converted from the current Iterable
• ->toImmVector(): ImmVector<Tv>
  Returns an immutable vector (ImmVector) converted from the current Iterable
• ->toValuesArray(): varray<Tv>
  Returns an array with the values from the current Iterable

Public Methods (HH\Collection)

• ->clear()
  Removes all items from the collection

Public Methods (OutputCollection)

• ->add(Te $e): this
  Add a value to the collection and return the collection itself
• ->addAll(?Traversable<Te> $traversable): this
  For every element in the provided Traversable, append a value into the current collection

Public Methods (SetAccess)

• ->remove(Tm $m): this
  Removes the provided value from the current Set