Type hinting when calling arbitrary functions (closures) in PHP

Question

Silex PHP microframework does a callback injection based on the automatic type hinting. For example, in Silex one can supply a Closure argument with arbitrary arguments like so:

$app->get('/blog/show/{postId}/{commentId}', function ($commentId, $postId) {
    //...
});
$app->get('/blog/show/{id}', function (Application $app, Request $request, $id) {
    //...
});
// following works just as well - order of arguments is not important
$app->get('/blog/show/{id}', function (Request $request, Application $app, $id) {
    //...
});

How do I do this? I'm not interested in getting parameter types as strings. I am looking for a "no strings" fully automatic solution. In other words,

For a number of possible arguments:

$possible_arguments = [
    new Class_A(), 
    new Class_B(), 
    new Class_C(), 
    new Another_Class, 
    $some_class
];

For a closure with any number of arbitrary arguments, that can only include those defined above only once:
```
$closure = function (Class_B $b, Another_Class, $a) {
    // Do something with $a and $b
};
```

I need to get only matching arguments in order to call the closure with them:

// $arguments is now [$possible_arguments[1], $possible_arguments[3]]
call_user_func_array($closure, $arguments);

They will be using [Reflection](http://php.net/manual/en/book.reflection.php). A closure is converted to an instance of the [Closure](http://php.net/manual/en/class.closure.php) class internally, reflection works on it just like any other object. You should be able to get the closure's argument list by inspecting the object's `__invoke()` method. — DaveRandom, Dec 20 '12 at 08:42

score 5 · Answer 1 · edited May 23 '17 at 12:16

My guess would be using reflection.

http://php.net/manual/en/class.reflectionparameter.php

Super simple example:

function pre($var)
{
    echo '<pre>' . var_export($var, true) . '</pre>';
}

interface TestInterface
{
}

class TestClass
{
    public function __construct(TestInterface $testArg)
    {
    }
}

function TestFunc(TestInterface $testArg)
{
}

// for a class...

$className = 'TestClass';
$methodName = '__construct';

$argNumber = 0;

$ref = new ReflectionParameter([$className, $methodName], $argNumber);

pre($ref);
pre($ref->getClass());



// for a function...
$funcName = 'TestFunc';
$argNumber = 0;

$ref = new ReflectionParameter($funcName, $argNumber);

pre($ref);
pre($ref->getClass());

Another question I found on stackoverflow might be a better answer to your question: PHP Reflection - Get Method Parameter Type As String

sanmai · Accepted Answer · 2012-12-21T02:50:45.313

Indeed they're using Reflection, specifically in the ControllerResolver class.

If you let me to simplify to include only one case of Closure and only object-type arguments:

$availableArguments = array($a, new B(), $c);
$arguments = array();
$reflection = new \ReflectionFunction($callback);  // $callback is a Closure
foreach ($reflection->getParameters() as $param) {
    if ($paramClass = $param->getClass()) {
        foreach ($availableArguments as $proposedArgument) {
            if ($paramClass->isInstance($proposedArgument)) {
                $arguments[] = $proposedArgument;
                break;
            }
        }
    }
}
call_user_func_array($callback, $arguments);

Type hinting when calling arbitrary functions (closures) in PHP

2 Answers2