Question 161400 in PHP Question posted in
Official manual can be found here.

Can a function parameter be optional for both an array & string using the same var?

I want to have a variable that is passed to my function as either an array or a string and have them optional. Here is the sample function:

function myFunction(string $msg = '' || array $msg = []) { // This is line 9
    if(is_string($msg)) {
        echo "I'm a string";
    } else if (is_array($msg)){
        echo "I'm an array";
    }
}

Is this possible? I can’t find anything that specifically shows this. When I try to run this function on a test page I get the following error:

Parse error: syntax error, unexpected variable "$msg", expecting "("
in /Path/To/My/File/test.php on line
9

I have looked at the php manual for function arguements: https://www.php.net/manual/en/functions.arguments.php and it states:

Information may be passed to functions via the argument list, which is
a comma-delimited list of expressions. The arguments are evaluated
from left to right, before the function is actually called (eager
evaluation).

So why wouldn’t what I wrote work?

Tags:

2

Answers


  1. 0

    It is posible, but the default value must be one of the types in your union type (Available since PHP 8.0):

    function myFunction(string|array $msg = [])

//OR

function myFunction(string|array $msg = '')
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  2. 0
    1. Composite Types: https://www.php.net/manual/en/language.types.declarations.php#language.types.declarations.composite
    2. Nullable Types: https://www.php.net/manual/en/language.types.declarations.php#language.types.declarations.nullable
    function myFunction(string|array $msg = NULL) {
    if( is_null($msg) ) {
        // do a default thing?
    }
    var_dump($msg);
}

myfunction();
myfunction('foo');
myfunction(['foo']);

    Output:

    NULL
string(3) "foo"
array(1) {
  [0]=>
  string(3) "foo"
}

    Note: Composite Types are only available in PHP>=8. To accomplish this in PHP<8 you would have to omit the type declaration completely, and implement the check yourself. Eg:

    function myFunction($msg = NULL) {
    if( ! in_array(gettype($msg), ['string', 'array', 'NULL']) ) {
        throw new Exception('Parameter msg not of an acceptable type.');
    }
    var_dump($msg);
}

    Though if you’re trying to accommodate "one or more" in a simplified manner I would suggest something like the following instead:

    function handleOne(string $msg) {
    echo $msg . PHP_EOL;
}

function handleMany(array $msgs) {
    foreach( $msgs as $msg ) {
        handleOne($msg);
    }
}

handleOne('first');
handleMany(['second', 'third']);

    Which has the additional benefit of ensuring that all the array members are strings, along with being much easier to maintain.

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