PHP is there a way to add elements calling a function from inside of array

Question

I want to add multiple values from inside of array calling a function:

$header = array(
  'name',
  'surname',
  _create_days(),
  'total'
);

So output be like

$header = array(
  'name',
  'surname',
  '2016-01-01',
  '2016-01-02',
  ....
  'total'
);

I've tried with array_push, array_merge but didn't work.

Answer 1

It doesn't work the way you wrote it in the question. The function _create_days() is called and it returns a value that replaces the function call. Even if the function returns multiple values in an array, the array as a whole is placed in the outer array you want to build.

The solution is to write the function _create_days() to return an array of values and merge this returned array into the outer array using array_merge() for example:

function _create_days()
{
    return array(
        '2016-01-01',
        '2016-01-02',
    );
}

$header = array_merge(
    array(
        'name',
        'surname',
    ),
    _create_days(),
    array(
        'total',
    )
);

Another option is to use a placeholder when you build $header and replace it later with the values returned by _create_days() using the function array_splice() :

$header = array(
    'name',
    'surname',
    '@days@',           // this is the placeholder
    'total',
);

// Replace the placeholder with the values returned by _create_days()
array_splice(
    $header,
    array_search('@days@', $header),
    1,
    _create_days()
);

In order to make the code flexible I used the function array_search() to find the position of the placeholder in $headers . This way, if you add or remove elements before '@days@' the code still works without any adjustment.

Answer 2

If you're willing to iterate through the array after you've created it, you can simply use special values for callbacks that you want to call:

Example:

<?php

function _create_days() {
    return [
        '2016-01-01',
        '2016-01-02',
    ];
}

$header = [
  'name',
  'surname',
  ['_create_days'], // We know it's a callback because it's an array
  'total',
];

$headerNew = [];

foreach ($header as $value) {
    if (is_array($value)) {
        // If the length of $value is above 1 then it's a class callback, else just set it to the first item
        $callback = count($value) > 1 ? $value : $value[0];

        // Get the actual array from the callback
        $value = call_user_func($callback);

        // Merge the $headerNew array with the new values
        $headerNew = array_merge($headerNew, $value);
    } else {
        // It's not a callback, just use the actual value
        $headerNew[] = $value;
    }
}

print_r($headerNew);

Output:

Array
(
    [0] => name
    [1] => surname
    [2] => 2016-01-01
    [3] => 2016-01-02
    [4] => total
)

DEMO

---

Note:

If you have any actual arrays in the $header array this makes things a little more difficult, as we can't check if you're using an array. For that you can simply create an instance of a class:

<?php

// (_create_days function)

class ValueCallback {
    protected $callback;

    public function __construct($callback) {
        if (is_array($callback)) {
            $callback = count($callback) > 1 ? $callback : $callback[0];
        }

        $this->callback = $callback;
    }

    public function getValue() {
        return call_user_func($this->callback);
    }
}

$header = [
  'name',
  'surname',
  new ValueCallback('_create_days'),
  'total',
];

$headerNew = [];

foreach ($header as $value) {
    if ($value instanceof ValueCallback) {
        // Get the actual array from the callback
        $value = $value->getValue();

        // Merge the $headerNew array with the new values
        $headerNew = array_merge($headerNew, $value);
    } else {
        // It's not a callback, just use the actual value
        $headerNew[] = $value;
    }
}

print_r($headerNew);

DEMO

Answer 3

From PHP7.4, just unpack/spread your function's return value directly into the result array with ( ... -- the spread operator).

Code: ( Demo )

function _create_days() {
    return ['2016-01-01', '2016-01-02'];
}

$header = [
    'name',
    'surname',
    ..._create_days(),
    'total',
];

var_export($header);

Output:

array (
  0 => 'name',
  1 => 'surname',
  2 => '2016-01-01',
  3 => '2016-01-02',
  4 => 'total',
)