Applicability analysis of array_fill_keys in multi-dimensional array initialization

When processing multidimensional arrays in PHP, initializing structures often requires certain skills. array_fill_keys is a very convenient function when initializing a one-dimensional associative array. It allows us to quickly generate an array through an array of key names and a unified initial value. However, when we need to initialize a multidimensional array , the applicability of array_fill_keys becomes worth discussing.

This article will introduce in detail the application methods and applicable scenarios of array_fill_keys in multi-dimensional array initialization, and analyze its limitations.

1. Introduction to array_fill_keys

 array array_fill_keys(array $keys, mixed $value)

This function receives two parameters:

• $keys : an array containing key names

• $value : The value that needs to be assigned to each key

Example:

 $keys = ['name', 'age', 'gender'];
$result = array_fill_keys($keys, null);

// Output result
print_r($result);

/*
Array
(
    [name] => 
    [age] => 
    [gender] => 
)
*/

This approach is very suitable for initializing one-dimensional arrays with a unified structure.

2. Application skills in multi-dimensional arrays

Although array_fill_keys itself cannot directly generate nested arrays (that is, it cannot initialize multidimensional structures), we can "disguised" the purpose of initializing multidimensional arrays by combining array_map or loops.

Example: Initialize a multidimensional array with a unified structure

Suppose we need to initialize a unified configuration structure for multiple users:

 $user_ids = [101, 102, 103];
$config_keys = ['theme', 'language', 'notifications'];

$default_config = array_fill_keys($config_keys, 'default');

$users = array_fill_keys($user_ids, []);

foreach ($users as $id => &$config) {
    $config = $default_config;
}
unset($config);

print_r($users);

/*
Array
(
    [101] => Array
        (
            [theme] => default
            [language] => default
            [notifications] => default
        )

    [102] => Array
        (
            [theme] => default
            [language] => default
            [notifications] => default
        )

    [103] => Array
        (
            [theme] => default
            [language] => default
            [notifications] => default
        )
)
*/

Or use array_map to implement it more concisely:

 $user_ids = [101, 102, 103];
$config_keys = ['theme', 'language', 'notifications'];

$default_config = array_fill_keys($config_keys, 'default');
$users = array_map(function() use ($default_config) {
    return $default_config;
}, array_fill_keys($user_ids, null));

print_r($users);

III. Applicability analysis

? Suitable scenarios:

• Initialize configuration data with consistent structure

• Quickly create a copy of a 1D array or 2D structure

• Form field preset value construction

? Limitations:

1. Nested initialization is not supported : multi-layer nested structures (such as third-level and fourth-level arrays) cannot be generated directly.

2. Quote Question : If the initialization value is an array or object without a deep copy, multiple keys will point to the same memory area, and modifying one value may affect all other items.

3. Key values ​​do not support dynamic nesting formats : for dynamic nesting key names, additional logical processing is required.

4. Alternative method suggestions

When array_fill_keys cannot meet the multidimensional array initialization requirements, the following alternatives can be considered:

• Building nested arrays using recursive functions

• Dynamically generate nested structures with array_reduce

• Initialization logical encapsulation using custom classes

5. Examples of practical application scenarios

Suppose you are building a user permission system, and each user's permission needs to be initialized to an empty collection, you can write it like this: