Evaluate `count()` once per loop instead of once per iteration by mukeshpanchal27 · Pull Request #12837 · WordPress/wordpress-develop

mukeshpanchal27 · 2026-08-04T12:03:15Z

Trac ticket: https://core.trac.wordpress.org/ticket/65811

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…eration. A `for` condition runs once per iteration plus once to terminate, so `$i < count( $array )` calls `count()` n + 1 times to walk an n-element array whose length never changes. Compute the bound in the loop initialiser instead, matching the idiom already used throughout core. `register_block_type_from_metadata()` is the main beneficiary: it runs for every registered block on every request, and the affected loops sit inside `foreach` blocks covering three script fields and three style fields each. In every case the iterated array is provably invariant across the loop body, so there is no behaviour change. Props mukesh.

github-actions · 2026-08-04T12:07:05Z

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github-actions · 2026-08-05T04:44:13Z

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Props mukesh27, westonruter, afercia.

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afercia · 2026-08-05T09:09:24Z

Thanks for your PR @mukeshpanchal27
It appears Claude missed something here. I would suggest to consider moving the call to count() outside the loop entirely. With the current approach, for example:

for ( $index = 0, $script_count = count( $scripts ); $index < $script_count; $index++ ) {

there's still one function call per loop iteration, it was just moved to the initialization part.

Instead, moving the count() outside the loop entirely and storing the result in a variable:

Eliminates any function calls during loop iterations.
Calls count() only once, before the loop starts.
Is more readable and clear in intent.
Provides maximum performance benefit.

$script_count = count( $scripts );
for ( $index = 0; $index < $script_count; $index++ ) {
    ...

…ss-develop into perf/hoist-count

mukeshpanchal27 · 2026-08-05T16:27:51Z

@afercia Thanks for the feedback it's not addressed. Please take a look when you have moment.

westonruter · 2026-08-06T19:26:15Z

+				$script_count = count( $scripts );
+				for ( $index = 0; $index < $script_count; $index++ ) {


Alternatively:

Suggested change

$script_count = count( $scripts );

for ( $index = 0; $index < $script_count; $index++ ) {

foreach ( range( 0, count( $scripts ) - 1 ) as $index ) {

However, given that range() doesn't use a generator, this means that the full array has to be in memory. But in reality, it's not many!

So I think this is a better approach.

Gemini share response:

These two approaches use entirely different paradigms—and in PHP, the second option (foreach with range()) introduces severe memory overhead and hidden performance issues.

Here is how they compare and why you should avoid range() for looping over arrays.

Comparison

for loop (Option 1): Fast and memory-efficient. Calculates array length once ($script_count) and iterates using standard integer incrementation.

foreach( range(...) ) (Option 2): Creates an entire second array in memory filled with integers from 0 to count($scripts) - 1 before the loop even starts.

Key Issues with foreach( range(...) )

1. Memory Overhead
If $scripts contains 10,000 items, range(0, 9999) allocates a brand-new array of 10,000 integers in RAM just to serve as the loop counter.

2. Off-by-One Bugs on Empty Arrays
If $scripts is empty (count($scripts) is 0), range(0, -1) will produce [0, -1]. Your loop will attempt to run twice instead of zero times, leading to Undefined array key warnings.

3. Unnecessary Complexity
Iterating over array indices with foreach + range defeats the purpose of foreach.

How many items are we talking about here, though?

The theoretical performance concern would be addressed by a generator, which I noted above that PHP doesn't use unfortunately. Nevertheless, I don't believe the number of items is particularly large.

That said, I don't feel strongly about using range().

Thanks! That said, can we mark this conversation as resolved?

It won't hurt, and changing it can reduce code smell so others don't raise this in the future.

I would suggest, however, that the count initializer be placed inside the for loop, like this:

for ( $index = 0, $script_count = count( $scripts ); $index < $script_count; $index++ ) {

Or for a common idiom for naming:

for ( $i = 0, $len = count( $scripts ); $i < $len; $i++ ) {

This can be found in core (via 3rd party libraries), for example:

wordpress-develop/src/wp-includes/SimplePie/src/IRI.php

Line 519 in f358f5e

for ($i = 1, $len = count($bytes); $i < $len; $i++) {

Another example:

wordpress-develop/src/wp-includes/formatting.php

Line 769 in f358f5e

for ( $i = 1, $c = count( $textarr ); $i < $c; $i += 2 ) {

There quite a few.

Initially i propose that 83e095b but based on the #12837 (comment) feedback i apply that suggestion.

I would suggest, however, that the count initializer be placed inside the for loop, like this:

Asking as a learning opportunity: what would be the advantage? That way, count() is called at each loop iteration and the same variable is set again and again at each loop iteration. That seems completely unnecessary to me. If there are other places where this pattern is in used, then I'd argue it should be imporved there as well.
I know there are many occurrences of similar patterns, also on the JS side. That doesn't mean they are entirely OK.

Once this is finalized, I'll open a separate PR to address the other occurrences. That's my plan as a follow-up.

westonruter

Suggestion to use range() instead for these instances.

mukeshpanchal27 and others added 2 commits July 30, 2026 20:42

Merge branch 'trunk' into perf/hoist-count

073ae0e

mukeshpanchal27 self-assigned this Aug 4, 2026

Merge branch 'trunk' into perf/hoist-count

83e095b

mukeshpanchal27 marked this pull request as ready for review August 5, 2026 04:44

mukeshpanchal27 and others added 3 commits August 5, 2026 21:32

Merge branch 'trunk' into perf/hoist-count

37fa950

Move count() out of the loop initialiser into a variable

79d89df

Merge branch 'perf/hoist-count' of github.com:mukeshpanchal27/wordpre…

13cdd71

…ss-develop into perf/hoist-count

westonruter reviewed Aug 6, 2026

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westonruter requested changes Aug 6, 2026

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Merge branch 'trunk' into perf/hoist-count

eaf9235

		$script_count = count( $scripts );
		for ( $index = 0; $index < $script_count; $index++ ) {

	$script_count = count( $scripts );
	for ( $index = 0; $index < $script_count; $index++ ) {
	foreach ( range( 0, count( $scripts ) - 1 ) as $index ) {

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Use of AI Tools

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github-actions Bot commented Aug 4, 2026

Test using WordPress Playground

Some things to be aware of

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afercia commented Aug 5, 2026

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Comparison

Key Issues with foreach( range(...) )

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mukeshpanchal27 commented Aug 4, 2026 •

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Key Issues with `foreach( range(...) )`