Recently, a thread starting with a simple question went OT and became a
different exchange starting [here](https://forum.nim-lang.org/t/3128/2#19739).
The short version:
"Methods (inheritance based dispatch) and concepts (user defined type classes
with VTable based dispatch) are two solutions to the same problem and we don't
really need both."
"But wait, there's a difference between the two: with inheritance, the author
of a derived type explicitly refers to the base type. That's probably a
conscious commitment to a contract of some kind. With a concept, the definition
of a matching type doesn't even mention the concept. So the match could be
coincidence and there's no commitment to a behavioral contract."
Two questions about this:
* Is this difference important enough to care about it?
* If it is (as I think), could there be a kind of concept which provides such
a contract commitment by the matching type?
The latter could look something like this:
type
MyConcept = explicit concept m
# the optional "explicit" means: only concrete types defined with
"satisfies"
# match.
...
MyType = object of BaseType satisfies MyConcept
# the optional "satisfies" means: I am consciously claiming to be a
MyConcept
# and I satisfy its contract.
...
If this makes any sense: should it be part of the language spec or implemented
as a macro?
