PHP の参照のあれ

PHP の参照のあれ

• PHPが糞言語なのはどう考えても参照をポインタだと思っているお前らが悪い - なんたらノート第三期ベータ

もっと単純にすると次の結果を比べると判りやすい。

<?php
call_user_func(function(){
    echo 'val_val' . PHP_EOL;

    $a = range(1, 100000);
    $m  = memory_get_usage();
    $b = $a;
    $c = $b;

    echo '  memory usage: ' . number_format(memory_get_usage() - $m) . PHP_EOL;
});

call_user_func(function(){
    echo 'ref_val' . PHP_EOL;

    $a = range(1, 100000);
    $m  = memory_get_usage();
    $b = &$a;
    $c = $b;

    echo '  memory usage: ' . number_format(memory_get_usage() - $m) . PHP_EOL;
});

call_user_func(function(){
    echo 'val_ref' . PHP_EOL;

    $a = range(1, 100000);
    $m  = memory_get_usage();
    $b = $a;
    $c = &$b;

    echo '  memory usage: ' . number_format(memory_get_usage() - $m) . PHP_EOL;
});

call_user_func(function(){
    echo 'ref_ref' . PHP_EOL;

    $a = range(1, 100000);
    $m  = memory_get_usage();
    $b = &$a;
    $c = &$b;

    echo '  memory usage: ' . number_format(memory_get_usage() - $m) . PHP_EOL;
});

結果 ... 3v4l.org。

val_val
  memory usage: 48
ref_val
  memory usage: 9,848,776
val_ref
  memory usage: 9,848,776
ref_ref
  memory usage: 48

もしくは、refcount と is_ref がどのようになるかを比べてみたり。

<?php
call_user_func(function(){
    echo 'val_val' . PHP_EOL;

    $a = "xxx";
    $b = $a;
    $c = $b;

    ob_start(function ($s) { return preg_replace('/^/m', "  ", $s); });
    xdebug_debug_zval('a', 'b', 'c');
    ob_end_flush();
});

call_user_func(function(){
    echo 'ref_val' . PHP_EOL;

    $a = "xxx";
    $b = &$a;
    $c = $b;

    ob_start(function ($s) { return preg_replace('/^/m', "  ", $s); });
    xdebug_debug_zval('a', 'b', 'c');
    ob_end_flush();
});

call_user_func(function(){
    echo 'val_ref' . PHP_EOL;

    $a = "xxx";
    $b = $a;
    $c = &$b;

    ob_start(function ($s) { return preg_replace('/^/m', "  ", $s); });
    xdebug_debug_zval('a', 'b', 'c');
    ob_end_flush();
});

call_user_func(function(){
    echo 'ref_ref' . PHP_EOL;

    $a = "xxx";
    $b = &$a;
    $c = &$b;

    ob_start(function ($s) { return preg_replace('/^/m', "  ", $s); });
    xdebug_debug_zval('a', 'b', 'c');
    ob_end_flush();
});

結果。

val_val
  a: (refcount=3, is_ref=0)='xxx'
  b: (refcount=3, is_ref=0)='xxx'
  c: (refcount=3, is_ref=0)='xxx'
ref_val
  a: (refcount=2, is_ref=1)='xxx'
  b: (refcount=2, is_ref=1)='xxx'
  c: (refcount=1, is_ref=0)='xxx'
val_ref
  a: (refcount=1, is_ref=0)='xxx'
  b: (refcount=2, is_ref=1)='xxx'
  c: (refcount=2, is_ref=1)='xxx'
ref_ref
  a: (refcount=3, is_ref=1)='xxx'
  b: (refcount=3, is_ref=1)='xxx'
  c: (refcount=3, is_ref=1)='xxx'