Can not parse seq of Components

[planetis-m]

import eminim, streams

type Component = ref object of RootObj
type Move = ref object of Component
  speed: float32
let s = newStringStream("""{"speed":20}""")
let a = Move(s.jsonTo(Component))
echo a.speed

From the marshal module docs:

Restriction: For objects, their type is not serialized. This means essentially that it does not work if the object has some other runtime type than its compiletime type.

[planetis-m]

possible "solution": create a complicated macro that can understand object hierarchy:

type Component = ref object of RootObj
type Move = ref object of Component
  speed: float32

s.jsonTo(Component < Move | (Transform < Hierarchy))

Generates code that will recreate dst each time it matches the signature of a type.

type
  ObjHierarchy = enum
    Component
    Move
    Transform
    Hierarchy

var
  runtimeType: set[ObjHierarchy] = {Component}
eat(p, tkCurlyLe)
while p.tok != tkCurlyRi:
  if p.tok != tkString:
    raiseParseErr(p, "string literal as key")
  case p.a
  of "speed":
    discard getTok(p)
    eat(p, tkColon)
    if runtimeType * {Move} != {Move}:
      if Transform in runtimeType:
        when defined(emiLenient):
          skipJson(p)
        else: raiseParseErr(p, "invalid object hierarchy")
      dst = Move(field1: dst.field1, ...) # Recreate dst
    initFromJson(dst.speed, p)
  else:
    raiseParseErr(p, "valid object field")
  if p.tok != tkComma:
    break
  discard getTok(p)
eat(p, tkCurlyRi)