Here I propose two small different changes: to refuse line 2 and accept line 4. Mutable static variables can't be used in pure functions, so it's better to really disallow them, and produce a compile error at line 2 here (there's no point in allowing their definition and disallowing just their usage). (On the other hand the static "z" at line 3 is a const and can be allowed, as dmd does now.) The compiler can also allow the line 4, because z will not change, keeping the function foo pure (there is no point in disallowing something that's semantically correct and safe). pure int foo(int x) { static int y = 10; // line 2 ERR const static int z = 20; // line 3 OK (as now) return x + z; // line 4 OK } void main() {}
https://github.com/D-Programming-Language/dmd/pull/194 This allows static and global value type variables to be used in pure functions. I'm not sure if disabling mutable static variables inside pure functions is valid, as some actions on them (eg. returning their address) do make sense. They can also be accessed from any statements inside debug {}. Please open a new report for that if you would like it.
https://github.com/D-Programming-Language/dmd/commit/b135734828b239e52ea95f34a59081b526d9fa5e
Thank you both for fixing the first thing. (In reply to comment #1) > I'm not sure if disabling mutable static variables inside pure functions is > valid, as some actions on them (eg. returning their address) do make sense. Returning the address of a static variable defined inside a pure function? I don't see the purpose of this. It smells. > They can also be accessed from any statements inside debug {}. But this need is probably uncommon, and when this needs arises you are able to move the definition of such variable inside the debug: pure int foo(int x) { debug { static int y = 10; } return x; } void main() {} > Please open a new report for that if you would like it. Maybe Walter is willing to comment on this, but I think I will open another report for this.
This was fixed a while ago.