# array_find_key

(PHP 8 >= 8.4.0)

array_find_key — Returns the key of the first element satisfying a callback function

### 说明

array_find_key(array `$array`, callable `$callback`): mixed

array_find_key() returns the key of the first element of an array for which the given `callback` returns `true`. If no matching element is found the function returns `null`.

### 参数

`array`
  The array that should be searched.
`callback`

  The callback function to call to check each element, which must be

  callback(mixed `$value`, mixed `$key`): bool
  If this function returns `true`, the key is returned from array_find_key() and the callback will not be called for further elements.

### 返回值

The function returns the key of the first element for which the `callback` returns `true`. If no matching element is found the function returns `null`.

### 示例

示例 #1 array_find_key() example

`<?php
$array = [
'a' => 'dog',
'b' => 'cat',
'c' => 'cow',
'd' => 'duck',
'e' => 'goose',
'f' => 'elephant'
];
// Find the first animal with a name longer than 4 characters.
var_dump(array_find_key($array, function (string $value) {
return strlen($value) > 4;
}));
// Find the first animal whose name begins with f.
var_dump(array_find_key($array, function (string $value) {
return str_starts_with($value, 'f');
}));
// Find the first animal where the array key is the first symbol of the animal.
var_dump(array_find_key($array, function (string $value, $key) {
return $value[0] === $key;
}));
// Find the first animal where the array key matching a RegEx.
var_dump(array_find_key($array, function ($value, $key) {
return preg_match('/^([a-f])$/', $key);
}));
?>`

以上示例会输出：

    string(1) "e"
    NULL
    string(1) "c"
    string(1) "a"

### 参见

- array_find() - Returns the first element satisfying a callback function
- array_all() - Checks if all array elements satisfy a callback function
- array_any() - Checks if at least one array element satisfies a callback function
- array_filter() - 使用回调函数过滤数组的元素
- array_reduce() - 用回调函数迭代地将数组简化为单一的值

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