On 20/08/13 19:27, Matt Calabrese wrote:
On Tue, Aug 20, 2013 at 6:11 AM, Mathias Gaunard < mathias.gaunard@ens-lyon.org> wrote:
His argument is that the definition of concepts and their association with types is not rigid and formal anymore. It's just any constant boolean expression. It's not a bug, it's a feature.
It's not a "bug" or "feature," it's a design choice that makes it difficult or impossible to add proper template definition checking in the future and it also makes writing template definitions that use the concept more difficult than the 0x approach. In ConceptsLite, rather than dealing with a direct list of associated functions (including their parameter list and explicit return type) and associated types, you instead have to deduce everything from usage requirements if you are to actually check a template definition or write any code that slightly deviates from the precisely written usage specification. Programmers are used to writing functions where their parameter types correspond to a type specification and 0x concepts was extremely similar to that. You look at a concept definition much like you would a type definition, see its functions and types, and you are set.
All existing C++ concepts have requirements specified as a list of valid expressions with the right properties, not with a class-like function list. The new approach is more fitting to concepts as they've been used in C++.