Ref

:::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. :::

Wrapper class for getting object (byref) semantics for a value type

This is especially useful for mutating values outside of a lambda's scope.

In general, it's preferable to refactor to use return values or inout parameters instead of using this class - however, a Ref of a Hack array is generally preferable to a Hack collection - e.g. prefer Ref<vec<T>> over Vector<T>.

C\reduce() and C\reduce_with_key() can also be used in some situations to avoid this class.

Interface Synopsis

namespace HH\Lib;

final class Ref {...}

Public Methods

• ->__construct(T $value)
• ->get(): T
  Retrieve the stored value
• ->set(T $new_value): void
  Set the new value