What does TypeError: in Type, in parameter, expected Type got xyz mean in Julia

Question

I'm trying to work on some code and this is the error that I'm getting.

TypeError: in Type, in parameter, expected Type got xyz

Can anyone explain to me what would theoretically cause this to happen? This error message doesn't help me at all. Thanks!

Answer 1

I was getting very similar error when incorrectly defining the return type of NamedTuples.

The correct way to do this is e.g.:

function fun(arg1::Int64, arg2::Float64)::NamedTuple{(:s1,:s2), Tuple{Int64, Float64}} 
    return (s1=arg1, s2=arg2) 
end

Also, it's useful to check the type of the instance you return to see the structure of the type signature, which you can then just copy-paste. E.g.

julia> typeof(fun(1, 2.))
NamedTuple{(:s1, :s2), Tuple{Int64, Float64}}