typetraits feature request - get subtype of a generic type

[mratsim]

I need to get the subtype of of generic parameter inside a function. I see that there is a genericHead in typetraits that get the "container". I would love to have a way to get the subtype.

seq[int].genericHead will be just seq

Use case, use TT.genericTail instead of "int" in the following proc

proc Foo[TT](a: TT): array[2, TT] =
  result[0] = newSeq[int](10)

Note this can also be solved with generic generics https://github.com/nim-lang/Nim/issues/3856

[mratsim]

Found a workaround with:

macro getSubType(T: typedesc): untyped =
  getTypeInst(T)[1][1]

proc Foo[TT](a: Node[TT]): array[2, TT] =
  result[0] = newSeq[getSubType(TT)](10)

[zah]

This issues was closed by accident, reopening.