PHP RFC: Chaining Comparison

• Version: 0.1
• Date: 2016-12-08
• Author: David Walker (dave@mudsite.com), Richard Fussenegger (php@fleshgrinder.com)
• Status: Draft
• First Published at: http://wiki.php.net/rfc/chaining_comparison

The point of this RFC is to allow the chaining together of [<, <=, >, >=] comparison operations to allow for easy range checking. Today, to determine if a variable is between two values you end up having to do two operations for the check, rather than a single check.

Today such comparisons must be written as such:

<?php
$a = 10;
 
if (0 < $a && $a < 100) {
    echo "Value is between 0 and 100\n";
}

The proposal of this RFC is to allow new syntax as follows:

<?php
$a = 10;
 
if (0 < $a < 100) {
    echo "Value is between 0 and 100\n";
}

This does not break any existing code

Next PHP (currently 7.2)

Yes, we're adding new JMP codes when chainging to ensure false values correctly jump over any pre/post inc/dev ops from eval.

Make sure there are no open issues when the vote starts!

This does not touch the other binary-op comparisons [==, ===, <=>]

Discuss if equality, or spaceship, would need this chaining: '$a == $b == $c' could be possible.

Requires 2/3 vote

Work In Progress: https://github.com/php/php-src/compare/master...bp1222:multi-compare

Will need eyes of those more familiar with AST/VM to review.

For changes affecting the core language, you should also provide a patch for the language specification.

Initial idea on Internals: http://marc.info/?l=php-internals&m=147846422102802&w=2

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