PHPの文字列と配列は実行可能？！？！

function example_func() {
  echo 'example_func was called';
}

'example_func'();
// example_func was called

class ExampleClass
{
    public static function example()
    {
        echo 'ExampleClass::example was called';
    }
}

['ExampleClass', 'example']();
// ExampleClass::example was called

function call_callback(callable $callback) {
    $callback();
}

// callableでタイプヒンティングされた引数に渡せる形式は3つあります

function example_func() {
  echo 'example_func was called';
}

class ExampleClass
{
    public static function example1()
    {
        echo 'ExampleClass::example1 was called';
    }

    public function example2()
    {
        echo 'ExampleClass::example2 was called';
    }

    public function __invoke()
    {
        echo 'ExampleClass was called';
    }
}

// 1.文字列
// 関数名
call_callback('example_func');
// example_func was called

// 静的メソッド
call_callback('ExampleClass::example1');
// ExampleClass::example1 was called


// 2.配列
// メソッド
call_callback([new ExampleClass, 'example2']);
// ExampleClass::example2 was called

// 静的メソッド
call_callback(['ExampleClass', 'example2']);
// ExampleClass::example1 was called


// 3.__invokeマジックメソッドを実装したオブジェクト
// オブジェクト
call_callback(new ExampleClass);
// ExampleClass was called

// 無名関数
call_callback(function () {
    echo 'closure was called';
});
// closure was called