How to Use Default Arguments in PHP Functions When You Only Want to Override Some of Them?

Using Default Arguments in PHP Functions

When assigning default values to function parameters in PHP, it's important to understand their limitations. Consider a function with parameters like:

<code class="php">function foo($blah, $x = "some value", $y = "some other value")</code>

What if you want to use the default argument for $x but specify a different value for $y?

Passing null for $x doesn't work because PHP interprets it as an intentional omission of a value. To address this, consider the following approach:

<code class="php">function foo($blah, $x = null, $y = null) {
    if (null === $x) {
        $x = "some value";
    }

    if (null === $y) {
        $y = "some other value";
    }

    // Code here!
}</code>

With this modification, you can call foo('blah', null, 'test') to use the default for $x and specify a custom value for $y.

It's important to note that PHP's default parameter mechanism applies to the last arguments in a function. If the desired argument isn't the last one, you can't omit the default arguments.

In situations where you want to handle varying parameter counts and types, you can consider a more flexible approach:

<code class="php">public function __construct($params = null)
{
    if ($params instanceof SOMETHING) {
        // Single parameter of type SOMETHING
    } elseif (is_string($params)) {
        // Single string argument
    } elseif (is_array($params)) {
        // Array of properties
    } elseif (func_num_args() == 3) {
        // 3 parameters passed
    } elseif (func_num_args() == 5) {
        // 5 parameters passed
    } else {
        throw new \InvalidArgumentException("Could not figure out parameters!");
    }
}</code>

This method provides greater flexibility in handling diverse input scenarios.

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