php - error when using variable class name and static method

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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

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 href="https://wiki.php.net/rfc/uniform_variable_syntax" rel="nofollow
noreferrer">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();

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Material: