Multiple dispatch doesn't find the correct method using `Type`

nsajko · June 5, 2024, 5:40pm

The first issue (your bug): unsupported manipulation with UnionAll:

This is not documented and I don’t think it’s correct. How did you come to this implementation? What’s the required behavior?

The second issue (arguably a Julia bug): inheriting from an abstract type doesn’t (currently) propagate parameter constraints. So this:

Should rather be:

struct RSAPOMDP1{S<:RSAState,A<:RSAAction} <: RSAPOMDP{S,A} end

That affects the dispatch for statetype1 etc.

Julia issue on Github:

github.com/JuliaLang/julia

The behavior of type parameter constraint inheritance is not documented

opened 10:11PM - 18 Feb 24 UTC

brainandforce

kind:breaking domain:types and dispatch kind:minor change

If you have an abstract type with a constrained type parameter, subtypes whose parameters inherit from the type's parameters do not inherit the constraints. ```julia abstract type AbstractFoo{T<:Real} end struct Foo{T} <: AbstractFoo{T} end ``` ```julia-repl julia> supertype(Foo) AbstractFoo{T} where T julia> supertype(Foo{<:Real}} AbstractFoo julia> Foo <: AbstractFoo # This one is very much unexpected! false julia> Foo{<:Real} <: AbstractFoo true ``` This is true even though you can't construct a type which violates the constraints on its parent's parameters: ```julia-repl julia> Foo{String} ERROR: TypeError: in AbstractFoo, in T, expected T<:Real, got Type{String} Stacktrace: [1] top-level scope @ REPL[5]:1 ``` This is a subtle point that is not included in the documentation on abstract parametric types, but has caused me some headaches when some subtype relations broke unexpectedly. The above examples were tested on Julia 1.10 (version info below) running on Arch Linux in WSL2, installed with the AUR provided `julia-bin` package that provides the official release: ```julia-repl julia> versioninfo() Julia Version 1.10.0 Commit 3120989f39b (2023-12-25 18:01 UTC) Build Info: Official https://julialang.org/ release Platform Info: OS: Linux (x86_64-linux-gnu) CPU: 20 × 13th Gen Intel(R) Core(TM) i5-13600K WORD_SIZE: 64 LIBM: libopenlibm LLVM: libLLVM-15.0.7 (ORCJIT, goldmont) Threads: 1 on 20 virtual cores ```

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Multiple dispatch doesn't find the correct method using `Type`

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