(PHP 5)
ReflectionParameter::__construct — Construct
$function
   , string $parameter
   )Constructs a ReflectionParameter class.
This function is currently not documented; only its argument list is available.
functionThe function to reflect parameters from.
parameterThe parameter.
No value is returned.
Example #1 Using the ReflectionParameter class
<?php
function foo($a, $b, $c) { }
function bar(Exception $a, &$b, $c) { }
function baz(ReflectionFunction $a, $b = 1, $c = null) { }
function abc() { }
$reflect = new ReflectionFunction('foo');
echo $reflect;
foreach ($reflect->getParameters() as $i => $param) {
    printf(
        "-- Parameter #%d: %s {\n".
        "   Class: %s\n".
        "   Allows NULL: %s\n".
        "   Passed to by reference: %s\n".
        "   Is optional?: %s\n".
        "}\n",
        $i, // $param->getPosition() can be used from PHP 5.2.3
        $param->getName(),
        var_export($param->getClass(), 1),
        var_export($param->allowsNull(), 1),
        var_export($param->isPassedByReference(), 1),
        $param->isOptional() ? 'yes' : 'no'
    );
}
?>
The above example will output something similar to:
Function [ <user> function foo ] {
  @@ /Users/philip/cvs/phpdoc/a 2 - 2
  - Parameters [3] {
    Parameter #0 [ <required> $a ]
    Parameter #1 [ <required> $b ]
    Parameter #2 [ <required> $c ]
  }
}
-- Parameter #0: a {
   Class: NULL
   Allows NULL: true
   Passed to by reference: false
   Is optional?: no
}
-- Parameter #1: b {
   Class: NULL
   Allows NULL: true
   Passed to by reference: false
   Is optional?: no
}
-- Parameter #2: c {
   Class: NULL
   Allows NULL: true
   Passed to by reference: false
   Is optional?: no
}