Bug 12611 – Deprecation and then error for implicit casts that lose precision in foreach index loops

In this program the assignment to x1 is accepted, but the assignments to x2 and x3 are refused: // Program #1. void main() { int[200] data1; ubyte x1 = data1.length; int[300] data2; ubyte x2 = data2.length; auto data3 = new int[300]; ubyte x3 = data3.length; } It gives (dmd 2.066alpha): test.d(5,16): Error: cannot implicitly convert expression (300u) of type uint to ubyte test.d(7,16): Error: cannot implicitly convert expression (data3.length) of type uint to ubyte Likewise the x2 case, this code is refused statically: // Program #2. void main() { int[300] data; foreach (ubyte i, x; data) {} // Error } test.d(3,5): Error: index type 'ubyte' cannot cover index range 0..300 But this code compiles and runs (and it seems to go in infinite loop): // Program #3. void main() { auto data1 = new int[300]; foreach (ubyte i, x; data1) {} int[300] data2; foreach (ubyte i, x; data2[]) {} } I think accepting silently the ubyte <- size_t assignment is bad and it goes against the behavour we expect from D as shown in the x2 and x3 cases. So I suggest to: 1) Give a warning in situations like program #3. (If you want you can also insert a run-time assert in non-release mode, that gards against the infinite loop with a clean run time error message. Perhaps Steven Schveighoffer has suggested something like this). 2) Turn the warning into a deprecation (and keep the run-time test, if already implemented). 3) Turn the deprecation into an error. If you want you can skip the first step, and introduce a deprecation already. See also Issue 9570

This has been deprecated. Closing as duplicate of 9570. *** This issue has been marked as a duplicate of issue 9570 ***