PHP, set default function parameter to result of function

Question

In PHP you can have optional parameters for a function:

public static function test($var = 'default string')

But I want to have the default value be the returned value from another function. For example I have a method called generateToken() that creates a random string of desired length. I attempted to execute the following code...

public static function sha512($token,$cost = 50000,$salt = self::generateToken(16)) {
        $salt = '$6$rounds=' . $cost . '$' . $salt . ' $';
        return crypt($token, $salt);
}

However this throws the following error...

Parse error: syntax error, unexpected '(', expecting ')' in /var/www/www.domain.com/path/to/cryptography.php on line 11

Line 11 is the method deceleration line. I am aware this could be done by setting the default to something like 'NONE' and then having an if statement call the method, but I would like to do it inside the method deceleration. How can I do this?

The documentation is clear: The default value must be a constant expression, not (for example) a variable, a class member or a function call. — Barmar
– Barmar, Commented Jan 31, 2015 at 17:34
The only work around that I see is using callbacks. php.net/manual/en/language.types.callable.php — Robert
– Robert, Commented Jan 31, 2015 at 17:37
@samyismyhero Would you like to post an answer with implementation using callbacks? Not sure how you would do this. — Hurricane Development
– Hurricane Development, Commented Jan 31, 2015 at 17:40

Hurricane Development · Accepted Answer · 2015-01-31 17:38:07Z

4

Says it right in the docs, this cannot be done.

So instead it must be implemented like the following...

public static function sha512($token,$cost = 50000,$salt = null) {
    $salt = ($salt == null) ? (self::generateToken(16)) : ($salt);
    $salt = '$6$rounds=' . $cost . '$' . $salt . ' $';
    return crypt($token, $salt);
}

answered Jan 31, 2015 at 17:38

Hurricane Development

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Shepmaster · Accepted Answer · 2015-01-31 19:13:49Z

0

public static function sha512($token,$cost = 50000,$salt) {
    $salt = self::generateToken(16);
    $salt = '$6$rounds=' . $cost . '$' . $salt . ' $';
    return crypt($token, $salt);
}

edited Jan 31, 2015 at 19:13

Shepmaster

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answered Jan 31, 2015 at 18:34

Daniel

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1 Comment

Shepmaster Over a year ago

Welcome to Stack Overflow! It's highly recommended that you include some prose that helps others understand why or how your solution solves the question.

Robert · Accepted Answer · 2015-01-31 20:06:30Z

public static function sha512( $token, $cost = 50000, $salt = null )

more specifically the $salt = null

But I want to have the default value be the returned value from another function.

Keeping to this intent this is not possible in PHP, PHP does not support first-class functions. The only workaround that I see as I mentioned in my comment above was the use of callbacks.

From what I understand the $salt param is intended to use what ever salt that you might like or default to the default one in your code.

So here is a possible solution although I believe you already answered your own question:

public static function sha512( $token, $salt = null, $cost = 50000 ) {

    // if a custom salt is provided
    if( isset( $salt ) ) {

        // calls the callback function passed in as a param
         $salt = $salt( 16 );

        // assemble the result to your specs
        $salt = '$6$rounds=' . $cost . '$' . $salt . ' $';

        // return final result
        return crypt( $token, $salt );
    }

    // default if no custom salt is provided
    $salt = self::generateToken( 16 );
    $salt = '$6$rounds=' . $cost . '$' . $salt . ' $';

    // return final result
    return crypt( $token, $salt );
}

The passed in callback must be in the current scope to be called successfully.

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