Better error messages - from reddit

[Nicholas Wilson]

On Tuesday, 5 March 2019 at 01:07:08 UTC, Walter Bright wrote:
> Use of `static if` and `pragma(msg)` can be used to generate 
> custom error messages:
>
>     static if (!isInputRange(r)) pragma(msg, r, " must be an 
> Input Range");

That doesn't work if you need to overload against it because then 
you will cause a matches multiple template error.

> This is ultimately far more powerful than anything the compiler 
> can come up with, because it can be about the user's context, 
> not the compiler's.

That power and flexibility does however severely limit the 
compiler's ability to provide sensible error messages, 99.9% of 
constraints are in CNF because thats the only  reasonable way to 
compose and perform overload specialisation.

The DIP covers all the cases.