PHP: rfc:sort_strict

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====== PHP RFC: SORT_STRICT Flag ======
  * Version: 0.1
  * Date: 2025-11-29
  * Author: Jason Marble, jmarble@intuitivetechnology.com
  * Status: Draft

===== Introduction =====

This RFC proposes ''SORT_STRICT'', a new flag that enables strict, type-aware comparison for PHP's sorting and array functions.

<PHP>
<?php

$values = [0, "", null, false, "0"];

var_dump(array_unique($values, SORT_STRICT));
// array(5) {
//   [0]=> int(0)
//   [1]=> string(0) ""
//   [2]=> NULL
//   [3]=> bool(false)
//   [4]=> string(1) "0"
// }

?>
</PHP>

PHP was famously created as a loosely typed language, prioritizing flexibility and ease of use. However, the introduction of strict types in PHP 7 marked a massive paradigm shift for the language. Over the last decade, the ecosystem has matured significantly; major frameworks like Symfony and Laravel, along with modern coding standards like PER, have effectively pushed strict typing from an optional feature to a de facto standard for professional PHP development.

Despite this evolution, there is no native way to sort or filter arrays without type coercion. The ''sort()'' family defaults to ''SORT_REGULAR'' (loose equality), while ''array_unique()'' defaults to ''SORT_STRING'' (string casting), neither of which distinguishes between values of different types. This creates a friction point where modern application logic is strict, but utility functions remain loose. Currently, developers wishing to filter unique values strictly or sort mixed-type arrays deterministically must implement userspace closures using ''usort'' or specific loops. This is verbose, slower than internal C implementations, and prone to error.

===== Proposal =====

Add a new constant ''SORT_STRICT'' that can be passed to the following functions:

  * **Value Sorting**: ''sort()'', ''rsort()''
  * **Associative Value Sorting**: ''asort()'', ''arsort()''
  * **Key Sorting**: ''ksort()'', ''krsort()''
  * **Multi-Array Sorting**: ''array_multisort()''
  * **Uniqueness**: ''array_unique()''

==== Comparison Logic: The "Strict Total Order" ====

''SORT_STRICT'' implements a two-step comparison:

=== Step 1: Compare Types ===

Values are first compared by their type according to this hierarchy:

<code>
NULL < Bool < Int < Float < String < Array < Object < Resource
</code>

If types differ, the comparison is decided here. No type coercion occurs.

=== Step 2: Compare Values ===

If types are identical, standard PHP comparison semantics apply:

^ Type     ^ Comparison Method                                                            ^
| NULL     | Always equal                                                                 |
| Bool     | ''false < true''                                                               |
| Int      | Numeric comparison                                                           |
| Float    | Numeric comparison                                                           |
| String   | Binary comparison (''strcmp'')                                                 |
| Array    | Standard array comparison, with ''SORT_STRICT'' applied recursively to elements |
| Object   | Standard object comparison, with ''SORT_STRICT'' applied recursively to properties |
| Resource | Resource ID comparison                                                       |

The key difference from ''SORT_REGULAR'' is that type coercion never occurs. An integer ''1'' and string ''"1"'' are never equal under ''SORT_STRICT'' because they differ at Step 1.

==== Examples ====

=== array_unique() ===

<PHP>
<?php

$values = [0, "", null, false, "0"];

var_dump(array_unique($values, SORT_REGULAR));
// array(2) {
//   [0]=> int(0)
//   [1]=> string(0) ""
// }

var_dump(array_unique($values, SORT_STRICT));
// array(5) {
//   [0]=> int(0)
//   [1]=> string(0) ""
//   [2]=> NULL
//   [3]=> bool(false)
//   [4]=> string(1) "0"
// }

?>
</PHP>

=== sort(): Order-Independent Value Matching ===

Compare arrays for identical values regardless of order:

<PHP>
<?php

$expected = [1, "1", true];
$actual = [true, 1, "1"];

sort($expected, SORT_STRICT);
sort($actual, SORT_STRICT);

var_dump($expected === $actual);
// bool(true)

?>
</PHP>

=== sort(): Homogeneity Verification ===

Because ''SORT_STRICT'' groups values by type, sorted data has a useful property: if the first and last elements share the same type, the array is homogeneous.

<PHP>
<?php

sort($data, SORT_STRICT);

$isHomogeneous = gettype(array_first($data)) === gettype(array_last($data));

?>
</PHP>

===== Backward Incompatible Changes =====

None. This RFC adds a new constant and does not modify existing behavior.

===== Proposed PHP Version(s) =====

Next PHP 8.x

===== RFC Impact =====

==== To the Ecosystem ====

IDEs, static analyzers, and language servers will need to recognize the new ''SORT_STRICT'' constant. No breaking changes are expected.

==== To Existing Extensions ====

None.

==== To SAPIs ====

None.

===== Open Issues =====

None currently.

===== Future Scope =====

  * A ''strict_compare($a, $b)'' function exposing the comparison logic directly
  * Support for ''SORT_STRICT'' in additional array functions (e.g., ''array_diff()'', ''array_intersect()'')

===== Voting Choices =====

Primary vote requiring a 2/3 majority:

<doodle title="Add SORT_STRICT flag as described in this RFC?" voteType="single" closed="true" closeon="YYYY-MM-DDTHH:MM:SSZ">
   * Yes
   * No
</doodle>

===== Patches and Tests =====

TODO: Link to implementation PR.

===== Implementation =====

TODO: After acceptance.

===== Rejected Features =====

None yet.

===== Changelog =====

  * 2025-11-29: Initial draft
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