[wp-trac] [WordPress Trac] #40192: apply_filters() works only once, if doing multiple array merge

[WordPress Trac]

#40192: apply_filters() works only once, if doing multiple array merge
--------------------------+-----------------------------
 Reporter:  esemlabel     |      Owner:
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  General       |    Version:  trunk
 Severity:  normal        |   Keywords:
  Focuses:                |
--------------------------+-----------------------------
 {{{#!php
 <?php
 $array = array( 'one', 'two' );
 $array = array_merge( $array, (array) apply_filters( 'example_filter',
 array() ) );
 }}}


 Such array_merge() need when we want only extend original array without
 modifying it. If we hook in this filter multiple times, the last one
 hooked functions will override all previously returned to filter values.

 {{{#!php
 <?php
 add_filter( 'example_filter', 'three' );
 function three() {
     return 'three';
 }

 add_filter( 'example_filter', 'four_n_five' );
 function four_n_five() {
     return array( 'four', 'five' );
 }
 }}}


 Result $array will be
 {{{#!php
 <?php
 $array = array( 'one', 'two', 'four', 'five' );
 }}}

 ------------------------------------------------------
 The only way to return all values is to always use original $array in
 apply_filters, and always perform array_merge() inside every hooked
 function. Look like the logic is gone.

 {{{#!php
 <?php
 $array = array( 'one', 'two' );
 $array = apply_filters( 'example_filter', $array );

 add_filter( 'example_filter', 'three' );
 function three( $array ) {
     return array_merge( $array, array( 'three' ) );
 }

 add_filter( 'example_filter', 'four_n_five' );
 function four_n_five( $array ) {
     return array_merge( $array, array( 'four', 'five' ) );
 }
 }}}


 Result $array will be
 {{{#!php
 <?php
 $array = array( 'one', 'two', 'three', 'four', 'five' );
 }}}

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Ticket URL: <https://core.trac.wordpress.org/ticket/40192>
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