Emulating named function parameters in PHP, good or bad idea?

Question

Named function parameters can be emulated in PHP if I write functions like this

function pythonic(array $kwargs)
{
    extract($kwargs);
    // .. rest of the function body
}

// if params are optional or default values are required
function pythonic(array $kwargs = array('name'=>'Jon skeet'))
{
    extract($kwargs);
    // .. rest of the function body
}

Apart from losing intellisense in IDEs what are the other possible downsides of this approach?

Edit:

Security: Shouldn't security be a non-issue in this case, as the extracted variables are limited to function scope?

Answer 1

I would suggest using the associative array to pass named parameters, but keep them in the array without extracting them.

function myFunc(array $args) {
    echo "Hi, " . $args['name'];
    // etc
}

There's a couple of reasons for this. Looking at that function, you can quite clearly see that I'm referring to one of the arguments passed into the function. If you extract them, and don't notice the extract() you (or the next guy) will be there scratching your head wondering where this "$name" variable came from. Even if you do know you're extracting the arguments to local variables, it's still a guessing game to a certain degree.

Secondly, it ensures that other code doesn't overwrite the args. You may have written your function expecting only to have arguments named $foo and $bar, so in your other code, you define $baz = 8;, for example. Later on, you might want to expand your function to take a new parameter called "baz" but forget to change your other variables, so no matter what gets passed in the arguments, $baz will always be set to 8.

There are some benefits to using the array too (these apply equally to the methods of extracting or leaving in the array): you can set up a variable at the top of each function called $defaults:

function myFunc (array $args) {
    $default = array(
        "name" => "John Doe",
        "age" => "30"
    );
    // overwrite all the defaults with the arguments
    $args = array_merge($defaults, $args);
    // you *could* extract($args) here if you want

    echo "Name: " . $args['name'] . ", Age: " . $args['age'];
}

myFunc(array("age" => 25)); // "Name: John Doe, Age: 25"

You could even remove all items from $args which don't have a corresponding $default value. This way you know exactly which variables you have.

Answer 2

Here's another way you could do this.

/**
 * Constructor.
 * 
 * @named string 'algorithm'
 * @named string 'mode'
 * @named string 'key'
 */
public function __construct(array $parameter = array())
{
    $algorithm = 'tripledes';
    $mode = 'ecb';
    $key = null;
    extract($parameter, EXTR_IF_EXISTS);
    //...
}

With this set up, you get default params, you don't lose intellisense in IDEs and EXTR_IF_EXISTS makes it secure by just extracting array keys that are already existing as variables.

(By the way, creating default values from the example you provided is not good, because if an array of param is provided without a 'name' index, your default value is lost.)

Answer 3

In my experience, this approach is really only beneficial if one of two things is true

1. For whatever extenuating reasons, your argument signature is big. I kinda go by 6 as a maximum - not for any specific reason though just seems right - but I freely admit that this number is arbitrary.
2. All or many of your arguments are optional, and sometimes you only need to set a value for the 5th one or some such thing. It's annoying to write someFunc( null, null, null, null, 1 );

If either of these is true for you, faking named params with an associative array might be the right implementation. Aside from knowing when to avoid extract (or avoiding it altogether) I can't immediately think of other downsides.

That being said, oftentimes both of these problems can be solved through refactoring as well.