Typing Question

General Usage
,
1

Hello!

Why is it that

Union{Missing, Float64} <: Union{Any}

yields

true

but

Matrix{Union{Missing, Float64}} <: Matrix{Union{Any}}

yields

false
2

Julia’s type system uses invariant type parameters.

You instead want

julia> Matrix{Union{Missing, Float64}} <: Matrix{<:Union{Any}}
true

or

julia> Matrix{<:Union{Missing, Float64}} <: Matrix{<:Union{Any}}
true
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3

This is an example of how Julia’s type parameters are invariant. This is discussed in some depth in Types · The Julia Language.

1 Like