Bug 4177 – __ctfe can't be used in pure functions

To define a std.math.log() function that works at compile time (see bug 3749 ) it can be used __ctfe, but there are problems: pure real log(real x) { if (__ctfe) return 0.0; else return 1.0; } enum x = log(4.0); void main() {} dmd v2.045 prints: test.d(2): Error: variable __ctfe forward referenced test.d(2): Error: pure nested function 'log' cannot access mutable data '__ctfe' test.d(7): Error: cannot evaluate log(4L) at compile time test.d(7): Error: cannot evaluate log(4L) at compile time I'd like __ctfe to work in pure functions too. I think it can be done because it's an immutable value that I think can't break the purity of the function/method, even if as in that example the function can give different outouts at compile and run time.

Since __ctfe is so magical and unique, it seems justified to give it one more special case. Other approaches I tried (changing the storage_class of __ctfe) were far more complicated. PATCH expression.c, VarExp::semantic(), line 4397. + /* Magic variable __ctfe never violates pure or safe + */ + if (v->ident == Id::ctfe) + return this; /* If ANY of its enclosing functions are pure, * it cannot do anything impure. * If it is pure, it cannot access any mutable variables other * than those inside itself */