Different PHP Callbacks

callbacks.php

<?php

// Examples for different uses of PHP callbacks

output(callback(function() { return 'anonymous function'; }));
output(callback('func'));
output(callback(new InvokableClass()));
output(callback([new NormalClass(), 'test']));
output(callback('StaticClass::staticMethod'));
output(callback([StaticClass::class, 'staticMethod']));
output(callback(['StaticClass', 'staticMethod']));
output(callback(InvokableClass::class));
output(callback(StringableClass::class));


// This prints out:

// anonymous function
// func
// InvokableClassInvokableClass::__invoke
// NormalClassNormalClass::test
// StaticClassStaticClass::staticMethod
// StaticClassStaticClass::staticMethod
// StaticClassStaticClass::staticMethod
// InvokableClassInvokableClass::__invoke
// StringableClassStringableClass::__toString


function callback($callable): string
{
    if (is_string($callable)) {
        if (function_exists($callable)) {
            return $callable();
        }
        if (class_exists($callable)) {
            $obj = (new $callable);
            if (is_callable($obj)) {
                return $obj();
            }
            if (method_exists($obj, '__toString')) {
                return $obj;
            }
        }
    }
    return $callable();
}

function func()
{
    return __FUNCTION__;
}

class StaticClass
{
    public static function staticMethod()
    {
        return __CLASS__ . __METHOD__;
    }
}

class NormalClass
{
    public function test()
    {
        return __CLASS__ . __METHOD__;
    }
}

class InvokableClass
{
    public function __invoke()
    {
        return __CLASS__ . __METHOD__;
    }
}

class StringableClass
{
    public function __toString()
    {
        return __CLASS__ . __METHOD__;
    }
}

function output(string $what): void
{
    echo $what . '<br>';
}