C++ vs. D , Ada and Eiffel (horrible error messages with templates)

Question

One of the problems of C++ are horrible error messages that we are getting from code which intensively uses templates and template metaprogramming. The concepts are designed to solve this problem, but unfortunately they will not be in the next standard.

I'm wondering, is this problem common for all languages, which are supporting generic programming? Or something is wrong with C++ templates?

Unfortunately I don't know any other language, that supports generic programming (Java and C# generics are too simplified and not as powerful as C++ templates).

So I'm asking you guys: are D,Ada,Eiffel templates (generics) producing such ugly error messages too? And Is it possible to have language with powerful generic programming paradigm, but without ugly error messages? And if yes, how these languages are solving this problem ?

Edit: for downvoters. I really love C++ and templates. I'm not saying that templates are bad. Actually I'm a big fan of generic programming and template metaprogramming. I'm just asking why I'm getting such ugly error messages from compilers.

Answer 1

In general I found Ada compiler error messages for generics really not significantly more difficult to read than any other Ada compiler error messages.

C++ template error messages, on the other hand, are notorious for being error novels. The main difference I think is the way C++ does template instantiation. The thing is, C++ templates are much more flexible than Ada generics. It is so flexible, it is almost like a macro preprocessor. The clever folks in Boost have used this to implement things like lambdas and even whole other languages.

Because of that flexibility, the entire template hierarchy basically has to be compiled anew every time its particular permutation of template parameters is first encountered. Thus issues that resolve down to incompatibilities several layers down a API end up being presented to the poor API client to decipher.

In Ada, Generics are actually strongly typed, and provide full information hiding to the client, just like normal packages and subroutines do. So if you do get an error message, it is typically just referencing the one generic you are trying to instatiate, not the entire hierarchy used to implement it.

So yes, C++ template error messages are way worse than Ada's.

Now debugging is a different story entirely...