Unhelpful error messages

[Peter Alexander]

On Sunday, 7 July 2013 at 06:58:29 UTC, Maxim Fomin wrote:
> http://d.puremagic.com/issues/

Ironically, this isn't helpful. H. S. Teoh is opening up a 
discussion, not reporting a bug.

The problem here is more general than this specific case. Any 
template constraint on any function could fail to pass, and the 
best error you'll get is that it couldn't match any function. 
Even if the error messages were improved to tell you what part of 
the constraint failed, you still have no idea *why* it failed 
(e.g. *why* is my range not a forward range?)

Overloads just make matters exponentially worse. Not only can the 
compiler fail to provide a good error for a single function, but 
needs to provide a good error for every possible candidate 
function. If a constraint checks if another overloaded function 
is callable then you end up with a combinatorial explosion of 
reasons why your function didn't compile.

It's a tough situation and I think the only way this could even 
reasonably be resolved is through some sophisticated IDE 
integration. There is no way to display this kind of error report 
in a blob of command line text.