Fix PHP warnings: undefined array key, property, offset etc.

php_undefined_key_property.php

<?php
/**
 * Access keys or properties of array or object
 * @variable array|object - array or object variable
 * @key_list array|string - list of keys, valid inputs are: ['key1', 'key2'], 'key1', 'key1->key2->key3', etc.
 * @default_value mixed, the default value to return if key/property does not exist
 */
function get_key($variable, $key_list, $default_value=null) {
    if (!isset($variable)) return $default_value;
    if (is_string($key_list)) {
        $multi = false;
        foreach (['->', '=>', '.', ','] as $sep) {
            if (strpos($key_list, $sep) !== false) {
                $key_list = explode($sep, $key_list);
                $multi = true;
                break;
            }
        }
        if (!$multi) $key_list = [$key_list];
    }
    $curr = $variable;
    foreach($key_list as $key) {
        if (is_object($curr)) $curr = $curr->$key ?? null;
        else if (is_array($curr)) $curr = $curr[$key] ?? null;
        else return $default_value;
        if (is_null($curr)) return $default_value;
    }
    return $curr;
}

// usage examples
class Foo {
    public $prop1 = 'prop1_val';
    public $prop2 = ['key' => 'val'];
    public $prop3 = [];
}
$cls = new Foo();
$cls->prop3 = ['cls' => new Foo()];
$arr1 = ['key1' => 'val1'];

echo get_key($arr1, 'key1').'<br>';
echo get_key($cls, ['prop3', 'cls', 'prop2', 'key']).'<br>';
echo get_key($cls, 'prop3->cls->prop2->key').'<br>';
echo get_key($cls, 'prop5->key1', 'default_val').'<br>';


/**
Output:
val1
val
val
default_val
*/