On Wednesday, 20 November 2013 at 23:27:38 UTC, Shammah
Chancellor wrote:
I just watched this talk from the goto conference by Walter
Bright (https://www.youtube.com/watch?v=cQkBOCo8UrE) and he
makes reference to "concepts." However, they look almost
identical to Protocols in Smalltalk -- something which I would
very much like to see in D.
It basically works much like an interface, but instead of
declaring it, you check the type to see if it defines the
appropriate methods.
"concept" is a term from C++ standard discussions which is a bit
closer to D and thus has priority ;)
In fact -- I believe this could be implemented today with
__traits and static foreach to simply check to see if a type
conforms to a protocol at compile time.
implementsProtocol!( R, InputRange!(int) );
where InputRange!() could just be a templated interface.
It has been implemented a dozen of times at the very least, I
have personally done it twice :D Key problem with having it as a
library type is that it
a) does not improve error messages at all over currently used
constraints (isInputRange!T) - it can be potentially fixed by
improving constraint error detection
b) it is impossible to do partial semantic validation of template
body based on concept limitation which is the original motivating
reason behind concept designs in C++ (with no success so far)
So yeah, it is neat, but not neat enough for anyone to actually
bother to push it into Phobos :) If you want to do it, it is
worth noting that you don't necessarily need to restrict to
templated interfaces, normal are also legit.
