On 6/11/17 11:11 AM, Nick Treleaven wrote:
On Sunday, 11 June 2017 at 00:28:58 UTC, Andrei Alexandrescu wrote:
https://github.com/dlang/phobos/pull/5461
There's many good advantages to this. The immediate one is the
constraint is better structured and easier to understand. Then, the
compiler can print the exact clause that failed, which improves the
precision and quality of the error message.
Great!
Thanks.
// Also possible (no change to the language)
enum bool isInputRange(R) =
is(typeof((ref R r) => r)) && msg("must be copyable")
&& is(ReturnType!((R r) => r.empty) == bool) && msg("must support
bool empty")
&& is(typeof(lvalueOf!R.front)) && msg("must support front")
&& is(typeof(lvalueOf!R.popFront)) && msg("must support back");
I'm not getting how this works.
Ostensibly the function is trivial:
bool msg(string) { return true; }
It doesn't change the semantics. The compiler would recognize it as an
intrinsic and would print the message if the clause to its left has failed.
Andrei
