How to Check Whether a Method Call Uses a Valid Class Constant

Question

I have a class where one method accepts an arguments that should be one of a specific range of options. I have defined these options as constants within the class. How do I prevent the method being called with a value that is not one of these constants?

Some code might make it clearer what I'm trying to achieve:

<?php
class Foo
{
    const OPTION_A = 'a valid constant';
    const OPTION_B = 'another valid constant';

    public function go( $option )
    {
        echo 'You chose: ' . $option;
    }
}

$myFoo = new Foo();
$myFoo->go( Foo::OPTION_A ); // ok
$myFoo->go( Foo::OPTION_B ); // ok
$myFoo->go( 'An invalid value' ); // bad - string, not one of the class constants
$myFoo->go( Bar::OPTION_A ); // bad - constant is not local to this class

You could use reflection and the ReflectionClass::getConstants method to achieve that. Have a look at the docs http://php.net/manual/en/reflectionclass.getconstants.php — Andreas, Nov 04 '16 at 09:14

score 1 · Accepted Answer · answered Nov 04 '16 at 09:23

1

Use ReflectionClass's getConstants() method:

public function go($option)
{
    $r = new \ReflectionClass($class);
    if (in_array($option, $r->getConstants()) {
        echo 'You chose: ' . $option;
    } else {
        echo 'urgh';
    }

}

answered Nov 04 '16 at 09:23

Attila Fulop

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I accepted this as it mostly solves the issue. However, if, in the example above, `Bar::OPTION_A` was the string `'a valid constant'`, your code would pass. How can I check the actually method call and be sure that the constant was from class `Foo` not class `Bar`? – voidstate Nov 04 '16 at 10:03
1

Short answer is you can't since constants aren't typed. One solution is to you use an enum, which is in fact a typed wrapper around class constants eg.: https://github.com/artkonekt/enum – Attila Fulop Nov 04 '16 at 10:08

How to Check Whether a Method Call Uses a Valid Class Constant

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