PHP用foreach来表达array_walk/array_filter/array_map/array_reduce

PHP装逼玩函数式(回调匿名函数):
array_walk/array_filter/array_map/array_reduce:
遍历数组,回调函数.遍历一次,回调一次.
这些逻辑其实均可以用foreach来表达,并且更容易理解.

array_walk至关于foreach:

$arr = ['Client'=>'jQuery','Server'=>'PHP'];
array_walk($arr, function($v, $k) {
    echo "键:$k 值:$v\n";
});

好比去除数组$arr元素的先后空白:

array_walk($arr, function(&$v) { $v = trim($v); });
foreach($arr as &$v) { $v = trim($v); }

array_filter: 用回调函数过滤数组中的单元,返回过滤后的数组
 

var_export(
    array_filter([1, 2, 3], function($v) {
        return $v > 1;
    })
);
和
foreach([1, 2, 3] as $k => $v) {
    if($v > 1) {
        $tmp[$k] = $v;
    }
}
var_export($tmp);
都输出:
array (
  1 => 2,
  2 => 3,
)

PHP数组映射化简(MapReduce):
array_map/array_reduce

array_map: 将回调函数做用到给定数组的单元上

var_export(
    array_map(function ($v) {
        return $v * $v;
    }, [1, 2, 3])
);
和
foreach([1, 2, 3] as $v) {
    $tmp[] = $v * $v;
}
var_export($tmp);
都输出:
array (
  0 => 1,
  1 => 4,
  2 => 9,
)

array_reduce: 用回调函数迭代地将数组简化(reduce)为单一的值

//输出16,即10+1+2+3,其中10做为初始值.
echo array_reduce([1, 2, 3], function($result, $item) {
    $result = $result + $item;
    return $result;
}, 10);
用foreach表达:
$result = 10;
foreach([1, 2, 3] as $v) {
    $result = $result + $v;
}
echo $result;