Bug 9909 – Overloaded foreach can not be used in pure functions

The following code does not compile if `func` is pure -------------------- struct Foo { int[3] arr = [1, 2, 3]; int opApply(int delegate(ref int) loopBody) { foreach(a; arr) loopBody(a); return 0; } } void func() // pure // Error! { Foo foo; int sum = 0; foreach(f; foo) { sum += f; } } void main() {} -------------------- Pure `func` can not call impure Foo.opApply. If `Foo.opApply` is pure then it can not call impure `loopBody`. If `loopBody` is pure then it can not modify "external" variable `sum`. If `sum` is defined inside loop body there is no error (even with `pure` keyword everywhere). So I guess DMD examines `foreach` body and finds it pure in that case. If that is true then taking into account purity of the function containing the loop could be a solution. In that case one would have to define two versions of opApply: for pure and not pure loop body.

Works since 2.067.1 if `opApply` and `loopBody` are marked as pure