Updating structs with type variables

[artemsolod]

Hi!

Thank you for this great package!

I've noticed that having type variable in a struct breaks things down.

struct A{T}
    x :: Int
end

a = A{:Foo}(1)
@set a.x = 2

ERROR: MethodError: no method matching A(::Int64)
Stacktrace:
 [1] macro expansion at /home/artem/.julia/packages/ConstructionBase/BMpJA/src/ConstructionBase.jl:0 [inlined]
 [2] setproperties at /home/artem/.julia/packages/ConstructionBase/BMpJA/src/ConstructionBase.jl:47 [inlined]
 [3] macro expansion at /home/artem/.julia/packages/Setfield/n9pIa/src/lens.jl:104 [inlined]
 [4] set(::A{:Foo}, ::Setfield.PropertyLens{:x}, ::Int64) at /home/artem/.julia/packages/Setfield/n9pIa/src/lens.jl:104
 [5] top-level scope at /home/artem/.julia/packages/Setfield/n9pIa/src/sugar.jl:166

This may lead to unexpected behaviour, if we had some additional constructor, e.g.

A(x :: Int) = (println("OMG OMG"); A{:Bar}(x))

results in

julia> @set a.x = 2
OMG OMG
A{:Bar}(2)

Although I might be misusing the package. Is there a workaround to handle type variables correctly?

[jw3126]

You are not misusing the package. I recommend to design A as described here. If that is not an option, consider overloading ConstructionBase.setproperties.

[jw3126]

@artemsolod is the issue resolved for you?

[artemsolod]

@jw3126, I understand this is expected behavior so I guess the issue is resolved, thank you!