Hi, Let’s assume that I have the following definition julia>abstract type Foo{T,U} end julia> typ = Foo{Int,Float64} Foo{Int64,Float64} julia> typ.parameters svec(Int64, Float64) #this is the function I would like to write julia>reconstruct_params(typ,(Float64,Float64)) Foo{Float64,Float64} H…

I think this is the same as was just asked: [image] Tricky parametric type dispatch General Usage I would like to dispatch a method like this, where T gets the type <: AbstractParticles and the type parameters end up in F and NT. function Base.union(p1::T{F,NT},p2::S{F,NS…

function reconstruct_params(::Type{T}, ::Type{U}, ::Type{V}) where {T,U,V} return T{U,V} end or, @generated function reconstruct_params(::Type{T}, ::Type{U}, ::Type{V}) where {T,U,V} return :(T{U,V}) end Both versions work with reconstruct_params(Foo, Float64, Float64)

But not with julia> reconstruct_params(Foo{Int,Int}, Float64, Float64) ERROR: TypeError: in Type{...} expression, expected UnionAll, got Type{Foo{Int64,Int64}} Stacktrace: [1] reconstruct_params(::Type{Foo{Int64,Int64}}, ::Type{Float64}, ::Type{Float64}) at ./REPL[1]:2 [2] top-level scope at none…

function reconstruct_params(::Type{Foo{S,T}}, ::Type{U}, ::Type{V}) where {S,T,U,V} return Foo{U,V} end

(Note though that this doesn’t extent to subtypes of Foo, which is what above link is about.)

What if I want to do this on general scale, What if I wouldn’t know the type and the number of parameters it is taking. Thanks

What actual problem are you trying to solve? Probably there is a better way to do it … it seems like you are fighting with the language to do something in a non-idiomatic way.

[image] Qiyamah: What if I want to do this on general scale, That’s what’s discussed in the link I posted. Maybe read that and then report back.

One can easily overload the function for that.

Sure, but in general you have to do it for each subtype, which is essentially what similar does for arrays (plus it also instantiates the type).

Type Reconstruction Question

General Usage

mauro3 April 12, 2019, 6:44pm 2

I think this is the same as was just asked:

Topic		Replies	Views
Tricky parametric type dispatch General Usage parametric-types	4	1125	April 12, 2019
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Feature: Higher order type constructors Internals & Design type , parametric-types	14	1262	February 20, 2021
Why can't i write such a function? General Usage	6	986	June 26, 2018
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Type Reconstruction Question

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