Is declaring a variable inside of calling a method bad practice?

Question

If I was to call a method which took a parameter, and then defined a variable at the same time, would that be considered "bad practice"?

Example:

if( file_exists( $file = "skins/Default/Controllers/Demo.php" ) )
{
    require( $file );
}

I feel as though it makes things easier as it doesn't require creating another variable above, nor does it clutter the code up by writing the string twice.

Answer 1

Is declaring a variable inside of calling a method bad practice?

Yes, because it hides the intent behind other functionality.

$file = "skins/Default/Controllers/Demo.php";
if (file_exists($file)) {
    require($file);
}

is easier to read and reason about than:

if (file_exists($file = "skins/Default/Controllers/Demo.php")) {
    require($file);
}

because it'd be easily mistaken for $file == "skins/Default/Controllers/Demo.php", which is common to see within an if statement.