I don't know the right answer to your problem. However note that a lot of
languages do not support multiple inheritance for a good reason (outside the
scope of this question), so how would you use those? A working pattern for me
is the following: create an interface to your "multi-interface" object:
type
Texture = ref object ...
AbstractRenderTarget = ref object {.inheritable.} ...
Window = ref object ...
proc setCurrentRenderTarget(t: AbstractRenderTarget)
proc renderTargetWithTexture(t: Texture): AbstractRenderTarget = ...
proc renderTargetWithWindow(w: Window): AbstractRenderTarget = ...
...
var myTexture: Texture = ...
setCurrentRenderTarget(renderTargetWithTexture(myTexture))
You could go a bit further and make renderTargetWithTexture and
renderTargetWithWindow implicit converters, so that setRenderTarget is just:
setRenderTarget(myTexture) # renderTargetWithTexture is called implicitly
Such pattern usually allows for a nice decoupled design, although may be a bit
problematic when you need to work with value types instead of reference types.
