Static variable assignment problems?

Static variable assignment problems? $ A = 100;
Static $ B = $;
Echo $ B;

Why can't I assign values to static variables like this?

Reply to discussion (solution)

$ B = 100;
Static $;
$ A = $ B;
Echo $;

Is that true?

Static attributes can only be initialized as a character value or a constant, and expressions are not allowed.
You can use static $ a = 'a'; or $ a = 100, but cannot perform value assignment or other expressions.

Static variables are created during php pre-compilation.
Therefore, normal variables cannot be assigned values because they are created during subsequent running periods.

To put it bluntly, you cannot assign a non-existent value to a static variable.

A static variable cannot be assigned a value directly to another variable. Only after the statement is declared.