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Evaluate count() once per loop instead of once per iteration #12837

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Evaluate count() once per loop instead of once per iteration #12837

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Editor, Themes: Evaluate count() once per loop instead of once per it…
mukeshpanchal27 Jul 30, 2026
073ae0e
Merge branch 'trunk' into perf/hoist-count
mukeshpanchal27 Aug 4, 2026
83e095b
Merge branch 'trunk' into perf/hoist-count
mukeshpanchal27 Aug 5, 2026
37fa950
Merge branch 'trunk' into perf/hoist-count
mukeshpanchal27 Aug 5, 2026
79d89df
Move count() out of the loop initialiser into a variable
mukeshpanchal27 Aug 5, 2026
13cdd71
Merge branch 'perf/hoist-count' of github.com:mukeshpanchal27/wordpre…
mukeshpanchal27 Aug 5, 2026
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Merge branch 'trunk' into perf/hoist-count
mukeshpanchal27 Aug 7, 2026
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9 changes: 6 additions & 3 deletions src/wp-includes/blocks.php
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Original file line number Diff line number Diff line change
Expand Up @@ -677,7 +677,8 @@ function register_block_type_from_metadata( $file_or_folder, $args = array() ) {
$scripts = $metadata[ $metadata_field_name ];
$processed_scripts = array();
if ( is_array( $scripts ) ) {
for ( $index = 0; $index < count( $scripts ); $index++ ) {
$script_count = count( $scripts );
for ( $index = 0; $index < $script_count; $index++ ) {
Comment on lines +680 to +681

@westonruter westonruter Aug 6, 2026

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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.

@mukeshpanchal27 mukeshpanchal27 Aug 7, 2026 •
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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.

@westonruter westonruter Aug 7, 2026

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How many items are we talking about here, though?

@westonruter westonruter Aug 7, 2026

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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().

@mukeshpanchal27 mukeshpanchal27 Aug 7, 2026

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

@westonruter westonruter Aug 7, 2026

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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++) {

@westonruter westonruter Aug 7, 2026

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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.

@mukeshpanchal27 mukeshpanchal27 Aug 7, 2026

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

@afercia afercia Aug 7, 2026

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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.

@mukeshpanchal27 mukeshpanchal27 Aug 7, 2026

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

$result = register_block_script_handle(
$metadata,
$metadata_field_name,
Expand Down Expand Up @@ -711,7 +712,8 @@ function register_block_type_from_metadata( $file_or_folder, $args = array() ) {
$modules = $metadata[ $metadata_field_name ];
$processed_modules = array();
if ( is_array( $modules ) ) {
for ( $index = 0; $index < count( $modules ); $index++ ) {
$module_count = count( $modules );
for ( $index = 0; $index < $module_count; $index++ ) {
$result = register_block_script_module_id(
$metadata,
$metadata_field_name,
Expand Down Expand Up @@ -747,7 +749,8 @@ function register_block_type_from_metadata( $file_or_folder, $args = array() ) {
$styles = $metadata[ $metadata_field_name ];
$processed_styles = array();
if ( is_array( $styles ) ) {
for ( $index = 0; $index < count( $styles ); $index++ ) {
$style_count = count( $styles );
for ( $index = 0; $index < $style_count; $index++ ) {
$result = register_block_style_handle(
$metadata,
$metadata_field_name,
Expand Down
3 changes: 2 additions & 1 deletion src/wp-includes/class-wp-theme-json.php
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Original file line number Diff line number Diff line change
Expand Up @@ -5386,7 +5386,8 @@ public function set_spacing_sizes() {

// If there are 7 or fewer steps in the scale revert to numbers for labels instead of t-shirt sizes.
if ( $spacing_scale['steps'] <= 7 ) {
for ( $spacing_sizes_count = 0; $spacing_sizes_count < count( $spacing_sizes ); $spacing_sizes_count++ ) {
$total_spacing_sizes = count( $spacing_sizes );
for ( $spacing_sizes_count = 0; $spacing_sizes_count < $total_spacing_sizes; $spacing_sizes_count++ ) {
$spacing_sizes[ $spacing_sizes_count ]['name'] = (string) ( $spacing_sizes_count + 1 );
}
}
Expand Down
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