'#subtype' directive

[renlite]

What exactly is #suptype directive doing? Didn't find aynthing in the docs.
It is used here: https://github.com/odin-lang/Odin/blob/master/vendor/directx/d3d11/d3d11.odin

[Hyrtwol]

lets say you have 2 structs

A :: struct {
...
}
B:: struct {
    #subtype a: A,
    ...
}
DoA :: proc (a: A) ...

b := B{}
DoA(b)

it makes is possible to call a proc that that takes the subtype as an argument without the need for a cast.
in d3d11 it's used to operate on the IUnknown for all the d3 objects

[renlite]

Is this inheritance?