> help us to define what Nim's type system actually is
Let's see.
type
Atype[T] = object
data : T
inum : int
Btype[T] = object
data : T
iinum : int
# Atype and Btype are isomorphic, however they do not have the same
field names
Stype[U] = Atype[U] or Btype[U]
# illtyped, 'a' does not necessarily have an 'inum'
proc stprint[T : Stype[string]] ( a : T) =
echo a.data," ",a.inum
# correctly typed, but...
proc stprint[T : Btype[int]] ( a : T) =
echo a.data," ",a.iinum
# type envelope for stprint not complete, Stype[int] is missing
proc tprint[T : Stype](a : T) =
stprint a
proc run() =
var vas = Atype[string]( data: "thatsit", inum : 7)
var vbi = Btype[int]( data: 42, iinum : 5 )
var vbs = Btype[string]( data: "youbetterdontcalltprintwithme", iinum :
12)
tprint(vas)
tprint(vbi)
#tprint(vbs)
echo vbs.data," ",vbs.iinum
run()
Run
This compiles silently. But is not correctly typed. If the compiler had to
build a virtual function table, it would complain (vft can't be constructed).
