How to Determine the Existence of Elements in an Array to Avoid Errors

Determining the Existence of Array Elements

When checking for the presence of an element within an array, the approach you described can lead to undefined index errors. To address this issue effectively, you can employ either the isset construct or the array_key_exists function.

Using isset

isset is the preferred option for speed optimization. It checks the existence of an element, regardless of its value. However, it returns false for elements that have been explicitly set to NULL.

Using array_key_exists

array_key_exists determines whether a specific key exists within an array. Unlike isset, it does not consider the value associated with the key.

Example:

Consider the following array:

<code class="php">$a = array(
    123 => 'glop',
    456 => null,
);</code>

Test with isset:

<code class="php">var_dump(isset($a[123])); // true (key exists with a non-null value)
var_dump(isset($a[456])); // false (key exists with a null value)
var_dump(isset($a[789])); // false (key does not exist)</code>

Test with array_key_exists:

<code class="php">var_dump(array_key_exists(123, $a)); // true (key exists regardless of value)
var_dump(array_key_exists(456, $a)); // true (key exists regardless of value)
var_dump(array_key_exists(789, $a)); // false (key does not exist)</code>

Code Update:

In your code, you can use isset to rewrite the check:

<code class="php">if (!isset(self::$instances[$instanceKey])) {
    $instances[$instanceKey] = $theInstance;
}</code>

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