FullyObservablePOMDP broken obsindex

[WhiffleFish]

obindex definition wrongly assumes that parametric type order for FullyObservablePOMDP is {S,A,...} when it really is {M,S,A}. Consequently, a method error is always raised.

POMDPs.jl/lib/POMDPTools/src/ModelTools/fully_observable_pomdp.jl

Line 6 in cc15fe9

struct FullyObservablePOMDP{M,S,A} <: POMDP{S,A,S}

POMDPs.jl/lib/POMDPTools/src/ModelTools/fully_observable_pomdp.jl

Line 17 in cc15fe9

POMDPs.obsindex(pomdp::FullyObservablePOMDP{S, A}, o::S) where {S, A} = stateindex(pomdp.mdp, o)

[lassepe]

Isn't the fix just to define

POMDPs.obsindex(pomdp::FullyObservablePOMDP{<:Any, S, A}, o::S) where {S, A} = stateindex(pomdp.mdp, o) 

[lassepe]

In fact, why are there any type parameters at all? Seems like we can just drop them in obsindex

[WhiffleFish]

Yeeeep it does seem unnecessary. The only reason I see to keep the state type parameter is to assert that the observation really is a valid state, preventing it from either failing silently or relying on stateindex to catch the type error.

[zsunberg]

Yeah, we should just get rid of S and A. We might want to accept observations that are not of type S, for example when S is a StaticVector but the user inputs a Vector.

This is an ancient leftover from the early days of Julia where you either needed those parameters or the coders (i.e. me) did not realize you didn't need them.

[WhiffleFish]

fixed by #485