Bug 9251 – An immutable arrays concatenation to produce an immutable implicitly castable to mutable?

void main() { string s1 = "abc"; char[] s2 = s1 ~ s1; } DMD 2.061alpha gives: test.d(3): Error: cannot implicitly convert expression (s1 ~ s1) of type string to char[] A concatenation allocates a new array, so I think it should be a strongly pure operation. So maybe a string concatenation should return a string that's implicitly castable to char[]. (While usually in D with purity you have mutable things that are implicitly castable to immutable). Is this possible and safe?

*** This issue has been marked as a duplicate of issue 1654 ***