Global variables read at compile time?

[Justin Whear]

On Wed, 15 Aug 2012 15:36:24 +0200, Stefan wrote:

> Hi there, I'm having trouble getting the following code to compile:
> 
> import std.stdio;
> 
> string a = "a";
> string b = a;
> 
> void main()
> {
>      writeln(b);
> }
> 
> DMD spits out the error "test.d(4): Error: variable a cannot be read at
> compile time". Is there any way to tell the compiler I want b evaluated
> at runtime, or am I missing something obvious here?

D is not as context-sensitive as what you may be used to. This is a 
feature to make the language more parseable and human-grokable. 
Basically, the result of a module-level assignment should not depend on 
what came before, so this example code is invalid:

string a = "a";
a = "b";
string b = a;

This would require the declaration of b to depend on the order of the 
declarations/statements which come before it.  When you add in the import 
of modules, things would get really hairy really fast. So module-level 
declarations must use constant expressions (literals or symbols to 
constant data) in their initialization.

Justin