On Saturday, 15 September 2018 at 15:31:00 UTC, Steven
Schveighoffer wrote:
The problem I had was that it wasn't clear to me which
constraint was failing. My bias brought me to "it must be
autodecoding again!". But objectively, I should have examined
all the constraints to see what was wrong. All C++ concepts
seem to do (haven't used them) is help identify easier which
requirements are failing.
They also make it so your automated documentation can post a link
to something that describes the type in more cases. std.algorithm
would still be relatively horked, but a lot of functions could be
declared as yielding, for instance,
ForwardRange!(ElementType!(TRange)).
We can fix all these problems by simply identifying the
constraint clauses that fail. By color coding the error message
identifying which ones are true and which are false, we can
pinpoint the error without changing the language.
I wish. I had a look at std.algorithm.searching.canFind as the
first thing I thought to check. Its constraints are of the form:
bool canFind(Range)(Range haystack)
if (is(typeof(find!pred(haystack))))
The compiler can helpfully point out that the specific constraint
that failed was is(...), which does absolutely no good in trying
to track down the problem.
