使用变量类名和静态方法时出错

Question

Running PHP 5.4, so I wasn't expecting this, but I'm encountering the following error:

Parse error: syntax error, unexpected '::' (T_PAAMAYIM_NEKUDOTAYIM)

Assume you have a variable of stdClass setup as follows:

$this->variable = new stdClass();

$this->variable->other = array('class' => 'helloworld');

Now, assume you want to access a static method of class helloworld:

// Standard call
$x = helloworld::my_static_method();

// Call with variable class name
$x = $this->variable->other['class']::my_static_method();

When calling the above using the variable class name, I receive the parsing error. What's odd, is that if I do the following, no error is presented:

$class = $this->variable->other['class'];

$x = $class::my_static_method();

To me this seems very odd, can anyone think of a reason why the class name isn't resolving correctly when using the first example versus the second?

Answer 1

can anyone think of a reason why the class name isn't resolving correctly when using the first example versus the second?

The PHP parser does not support such a syntax, and that's merely all. This is because the parser has grown historically. I can't give more reason than that.

It will be that with PHP 7 you can see some changes on these syntax details working more into your expected direction Uniform Variable Syntax:

($variable->other['class'])::my_static_method();

But until then, you can go around that with the help of call_user_func:

call_user_func([$variable->other['class'], 'my_static_method']);
call_user_func($variable->other['class'] . '::my_static_method');

Or as you wrote your own, by creating a variable:

$class = $variable->other['class'];
$class::my_static_method();

Or even a variable that looks like something different:

${(int)!${0}=$variable->other['class']}::my_static_method();

Related Material:

• Interpolation (double quoted string) of Associative Arrays in PHP