:::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. :::

Create a function reference to a global function

namespace HH;

function fun(
  string $func_name,
);

The global function fun('func_name') creates a reference to a global function.

The parameter 'func_name' is a constant string with the full name of the global function to reference.

Hack provides a variety of methods that allow you to construct references to methods for delegation. The methods in this group are:

• class_meth for static methods on a class
• fun for global functions
• inst_meth for instance methods on a single object
• meth_caller for an instance method where the instance will be determined later
• Or use anonymous code within a lambda expression.

Example

<?hh // strict
$v = vec["Hello", " ", "World", "!"];

// Each line below prints "Hello World!"
Vec\map($v, fun('printf'));
Vec\map($v, $x ==> { printf($x); });

Parameters

• string $func_name A constant string with the name of the global method, including namespace if required.

Returns

• $func - A fully typed function reference to the global method.