PHP call_user_func vs. just calling function

Question

I\'m sure there\'s a very easy explanation for this. What is the difference between this:

function barber($type){
    echo \"You wanted a $type haircut, no         


        

Answer 1

When using namespaces, call_user_func() is the only way to run a function you don't know the name of beforehand, for example:

$function = '\Utilities\SearchTools::getCurrency';
call_user_func($function,'USA');

If all your functions were in the same namespace, then it wouldn't be such an issue, as you could use something like this:

$function = 'getCurrency';
$function('USA');

Edit: Following @Jannis saying that I'm wrong I did a little more testing, and wasn't having much luck:

Bar: ".\Foo\Bar::getBar()."";
    // outputs 'Bar: Bar'
    $function = '\Foo\Bar::getBar';
    echo "
Bar: ".$function()."
";
    // outputs 'Fatal error: Call to undefined function \Foo\Bar::getBar()'
    $function = '\Foo\Bar\getBar';
    echo "
Bar: ".$function()."
";
    // outputs 'Fatal error: Call to undefined function \foo\Bar\getBar()'
}

You can see the output results here: https://3v4l.org/iBERh it seems the second method works for PHP 7 onwards, but not PHP 5.6.