I did not dive deeply into concepts as they are not yet "stable" but I think
this shows a bit how simple generics and concepts differ.
# a simple concept example
type Countable = concept c
inc c
dec c
type Foo = object
v: int
s: string
proc inc(a: var Foo) =
a.v += 1
proc dec(a: var Foo) =
a.v -= 1
proc twoForOneBackConcept(a: Countable): Countable =
result = a
inc result
inc result
dec result
proc twoForOneBackGeneric[T](a: T): T =
result = a
inc result
inc result
dec result
echo twoForOneBackConcept(1)
echo twoForOneBackGeneric(1)
echo twoForOneBackConcept('a')
echo twoForOneBackGeneric('a')
var x = Foo(v: 4, s: "Test")
echo twoForOneBackConcept(x)
echo twoForOneBackGeneric(x)
when false:
echo twoForOneBackConcept("Test") # will fail in this line
echo twoForOneBackGeneric("Test") # will fail at "inc" in the proc
