A Vision on Improved DMD Template Instantiation Diagonostics

[Xinok via Digitalmars-d]

On Friday, 12 June 2015 at 12:20:58 UTC, Per Nordlöw wrote:
> ...
>
> Destroy.

Improving compiler diagnostics for failed template instantiations 
would be a great start. However, template constraints in D are 
much more powerful and flexible than C++ concepts. As such, there 
are bound to be several cases in which the compiler can't provide 
any useful information, no matter how "smart" it may be.

In general, I think it needs to be easier for us programmers to 
produce our own error messages specifying why the template failed 
to instantiate. One trick that I use, which others have mentioned 
in other threads, is to use static asserts to find the exact 
condition that failed and print an informative error message.

Another idea I've mentioned before is to make it easy to define a 
"default" instance when none of the template constraints are 
satisfied. This would be a good place to insert some diagnostics 
to determine why the template instantiation failed and provide a 
meaningful error message.

A crude example:

     int foo(T)(T arg) if(...){ }
     int foo(T)(T arg) if(...){ }
     int foo(T)(T arg) default // Used when all other instances 
fail
     {
         // Insert diagnostics here
         static assert(isRandomAccessRange!T, "...");
         ...
     }