Purpose of Static Class Functions in PHP

Question

I thought that the use of the static keyword in the declaration of a class function meant that you could call the function without an instance of the class using the scope resolution operator (::).

For example:

class Foo
{
    public static function static_function() {
        return 'x';
    }
    public function non_static_function() {
        return 'y';
    }
}

// to call static_function:
echo Foo::static_function();

// to call non_static_function:
$foo = new Foo();
echo $foo->non_static_function();

The PHP.net documentation on static seems to support this idea.

I came across some code yesterday that someone had wrote accessing class functions using the scope resolution operator that had NOT been defined with the static keyword. I was surprised and confused to see this worked.

Given my class defined above, Foo, it turns out you can actually do:

echo Foo::static_function();
echo Foo::non_static_function();

Resulting in output xy without generating any errors or warnings.

If you can access non-static class functions without the static keyword, what is the point in it?

Answer 1

Resulting in output xy without generating any errors or warnings.

No way. The error reporting must have been turned off on that environment. That would have definitely produced a Strict Standards warning notice.