Template constraints

[bearophile via Digitalmars-d]

Observe:

https://github.com/D-Programming-Language/phobos/pull/3054

Is this change the partial proof of another failure of a part of 
D language design? What's the point of template constraints? 
Aren't C++ Concepts better? Or to rephrase that in a less 
trollish way, can D be enhanced to add user-defined error 
messages to template constraints, and is such enhancement a good 
idea?

Bye,
bearophile