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splice

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.

Return the string with a slice specified by the offset/length replaced by the given replacement string

namespace HH\Lib\Str;

function splice(
  string $string,
  string $replacement,
  int $offset,
  ?int $length = NULL,
): string;

If the length is omitted or exceeds the upper bound of the string, the remainder of the string will be replaced. If the length is zero, the replacement will be inserted at the offset.

Offset can be positive or negative. When positive, replacement starts from the beginning of the string; when negative, replacement starts from the end of the string.

Some examples:

  • Str\splice("apple", "orange", 0) without $length, $string is replaced, resolving to "orange"
  • Str\splice("apple", "orange", 3) inserting at $offset 3 from the start of $string resolves to "apporange"
  • Str\splice("apple", "orange", -2) inserting at $offset -2 from the end of $string resolves to "apporange"
  • Str\splice("apple", "orange", 0, 0) with $length 0, $replacement is appended at $offset 0 and resolves to "orangeapple"
  • Str\splice("apple", "orange", 5, 0) with $length 0, $replacement is appended at $offset 5 and resolves to "appleorange"

Previously known in PHP as substr_replace.

Guide​

Parameters​

  • string $string
  • string $replacement
  • int $offset
  • ?int $length = NULL

Returns​

  • string