Php: can't assign a property value in declaration

Question

I do not understand the rationale behind the different treatment of variable assignment between global context and class context:

$var1 = \"a\" . \"b\"; # PH         


        

Answer 1

Quoting from the PHP docs (my emphasis)

This declaration may include an initialization, but this initialization must be a constant value -- that is, it must be able to be evaluated at compile time and must not depend on run-time information in order to be evaluated.

Instead, define values in the constructor if they're dependent on any evaluation.