The proc needs to return a concrete type, while you're trying to return
Something, which is a type class. You'll be better here with either runtime
dispatch (`ref object` hierarchy + `methods`) or variant objects.
# runtime dispatch
type
Something = object
a: int
special: Special
Special = ref object {.inheritable.}
SpecialisedTA = ref object of Special
c: int
SpecialisedTB = ref object of Special
d: int
method foo(s: Special) {.base.} = assert(false, "Kinda abstract")
method foo(s: SpecialisedTA) = echo "SpecialisedTA"
method foo(s: SpecialisedTB) = echo "SpecialisedTB"
proc doIt(strategy: int): Something =
if (...):
result = Something(a: 10, special: SpecialisedTA(c: 30))
else:
result = Something(a: 10, special: SpecialisedTB(d: 10))
let myThing = doIt(...)
myThing.special.foo()
Run
# variant object
type
SpecialKind = enum
TA
TB
Something = object
a: int
case kind
of TA:
specialA: SpecialisedTA
of TB:
specialB: SpecialisedTB
SpecialisedTA = object
c: int
SpecialisedTB = object
d: int
proc doIt(strategy: int): Something =
if (...):
result = Something(a: 10, kind: TA, specialA: SpecialisedTA(c: 30))
else:
result = Something(a: 10, kind: TB, specialB: SpecialisedTB(d: 10))
let myThing = doIt(...)
case myThing.kind
of TA:
echo "SpecialA: ", myThing.specialA
of TB:
echo "SpecialB: ", myThing.specialB
Run
