replace_with

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.

Returns $haystack with any substring matching $pattern replaced by the result of $replace_func applied to that match

namespace HH\Lib\Regex;

function replace_with<T as Match>(
  string $haystack,
  Pattern<T> $pattern,
  (function(T): string) $replace_func,
  int $offset = 0,
): string;

If $offset is given, replacements are made only starting from $offset. The regex pattern follows the PCRE library: https://www.pcre.org/original/doc/html/pcresyntax.html.

Throws InvariantException if $offset is not within plus/minus the length of $haystack.

Guide

• String

Parameters

• string $haystack
• Pattern<T> $pattern
• (function(T): string) $replace_func
• int $offset = 0

Returns

• string