How to call constructor of parametric family of types efficiently

General Usage Performance
5

This is a relatively hard problem, see e.g. the discussion on Stripping parameter from parametric types here on discourse, or the paragraph on Design Patterns with Parametric Methods in the documentation.


I would think that building a separate method for each family remains the most idiomatic solution. This is more or less what similar does, for example.



That being said, if you really want a fully generic implementation, something like this might work:

stripped_type(x) = stripped_type(typeof(x))
stripped_type(typ::DataType) = Base.typename(typ).wrapper

For example:

julia> struct A{T}
           x::T
       end

julia> a = A(42)
A{Int64}(42)

julia> stripped_type(a)(42.5)
A{Float64}(42.5)

Again, I would not recommend such a solution, which relies too much on internal details to my taste.

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