PHP RFC: Add is_assoc_array

Version: 0.9
Date: 2026-02-21
Author: Muhammed Arshid, arshidkv12@gmail.com
Status: Under Discussion
Implementation: https://github.com/php/php-src/pull/21266

Introduction

PHP arrays can behave as both lists and associative maps. Currently, PHP has no built-in function to detect whether an array is associative.

Userland frameworks implement helper functions for this purpose. Adding a native function improves performance, readability, and consistency.

<?php
 
$data = ['a'=> 1, 'b' => 2];
var_dump(is_assoc_array($data)); // bool(true)
 
?>

Proposal

Add a new core function:

<?php
 
function is_assoc_array(array $array): bool {}
 
?>

This function determines whether an array is associative based on PHP’s internal array storage.

An array is considered associative when it is not a packed array internally.

Examples

<?php
 
var_dump(is_assoc_array(['a' => 'a', 0 => 'b']));   // true
var_dump(is_assoc_array([1 => 'a', 0 => 'b']));     // true
var_dump(is_assoc_array([1 => 'a', 2 => 'b']));     // true
var_dump(is_assoc_array([0 => 'a', 1 => 'b']));     // false
var_dump(is_assoc_array(['a', 'b']));               // false
 
var_dump(is_assoc_array([]));                      // false (empty array not associative)
var_dump(is_assoc_array([1, 2, 3]));               // false
var_dump(is_assoc_array(['foo', 2, 3]));           // false
 
var_dump(is_assoc_array([0 => 'foo', 'bar']));        // true
var_dump(is_assoc_array([1 => 'foo', 'bar']));        // true
var_dump(is_assoc_array([0 => 'foo', 'bar' => 'baz']));     // true
var_dump(is_assoc_array([0 => 'foo', 2 => 'bar']));        // true
var_dump(is_assoc_array(['foo' => 'bar', 'baz' => 'qux'])); // true
 
?>

Why This is Needed

Developers frequently need to check array type:
JSON encoding logic
API validation
Config parsing
Data normalization

Userland solutions are slower and inconsistent. Native implementation provides:

O(1) performance
Standard behavior
Cleaner code

Backward Incompatible Changes

None This adds a new function only.

Proposed PHP Version(s)

PHP 8.6

RFC Impact

There may be conflicts if userland code already defines is_assoc_array(). Such functions can be replaced with the built-in implementation.

No impact to SAPIs or OPcache.

Voting Choices

Pick a title that reflects the concrete choice people will vote on.

Please consult the php/policies repository for the current voting guidelines.

Primary Vote requiring a 2/3 majority to accept the RFC:

Implement $feature as outlined in the RFC?
Real name	Yes	No	Abstain
Final result:	0	0	0
This poll has been closed.

Patches and Tests

Links to proof of concept PR.

If there is no patch, make it clear who will create a patch, or whether a volunteer to help with implementation is needed.

Implementation

After the RFC is implemented, this section should contain:

the version(s) it was merged into
a link to the git commit(s)
a link to the PHP manual entry for the feature

References

Links to external references, discussions, or RFCs.

Rejected Features

Keep this updated with features that were discussed on the mail lists.

Changelog

If there are major changes to the initial proposal, please include a short summary with a date or a link to the mailing list announcement here, as not everyone has access to the wikis' version history.