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Editorial Team
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Asked: 2026-05-12T22:05:15+00:00

Is the ‘copy’ of an array for a foreach (of php5, in this case)

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Is the ‘copy’ of an array for a foreach (of php5, in this case) an immediate copy with actual overhead, or merely a lazy copy (copy on write) which only produces overhead if it detects a write manipulation?

The alternative, note in several places, is to run foreach over keys($array) — how can that really be faster?

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1 Answer

  1. Editorial Team

    OK, so I went off and measured it —

    Test This                    And This                       And, uh, This      
---------------------------  ----------------------------   ----------------------------
Setup                        Setup                          Setup                     
---------------------------- ----------------------------   ----------------------------
$i = array_fill(0,1000,'1'); $j = array_fill(0,1000,'1');   $j = array_fill(0,1000,'1');
$c = 0;                      $d = 0;                        $e = 0;
---------------------------  ----------------------------   ---------------------------
Code Under Test              Code Under Test                Code Under Test                    
---------------------------  ------------------------------ --------------------------
foreach ($i as $v)           foreach (array_keys($j) as $k) foreach ($i as &$v)
{ $c+= $v; }                 { $d+= $j[$k]; }               { $e+= $v; }    
---------------------------  ------------------------------ -------------------------
Tear Down                    Tear Down                      Tear Down                          
---------------------------  -----------------------------  -------------------------
print "c = $c";             print "d = $d";                 print "e = $e";                    
---------------------------- -----------------------------  --------------------------
Test for repetitions.  10000         
---------------------------- -----------------------------  -------------------------
c = 10000000                 d = 10000000                   e = 10000000
---------------------------- -----------------------------  -------------------------
Ran in  1.8540189266205      Ran in 4.0039160251617         Ran in 1.9633851051331
---------------------------  -----------------------------  -------------------------
Winner -0.10936617851257     Looser 2.0405309200287         2nd Best             0
---------------------------  ----------------------------  -------------------------

    Looks like foreach ($a as $v) is much better than array_keys and that using &v is in the middle.

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