I found this approach in Rotations.jl. Why code it this way? Note that AngleAxis is a concrete type, so AA can only be one type. @inline function (::Type{AA})(q::QuatRotation) where AA <: AngleAxis w = real(q.q) x, y, z = imag_part(q.q) s2 = x * x + y * y + z * z sin_t2 = sqrt(s2) …

No the signatures look the same AFAICT. These aren’t really callable structs. It is a strange way to write a constructor, but I can’t seem to find a difference. This can be used to do certain “Abstract” constructors but AngleAxis is a struct so I’m not sure the purpose.

I understand they are callable structs, but how are these three functions [image] prittjam: # Trivial type conversions for RotX, RotY and RotZ @inline function (::Type{AA})(r::RotX) where AA <: AngleAxis return AA(r.theta, 1, 0, 0) end @inline function (::Type{AA})(r::RotY) where AA <: Angl…

So I did some basic tests with these two idioms: outer constructor and type functor and indeed I can see no difference in how they are working in the context cited above. So I will mark it as correct, but maybe someone will see this and explain the use case more. Thanks!

I’ve seen this around and never found out why people write ::Type{X} in the callable position, it doesn’t seem to make a difference: julia> abstract type Y end julia> struct X<:Y end julia> (::Type{X})(::Int) = 1 julia> (::Type{blah})(::Float64) where blah<:X = 1.2 julia> (::Type{blah})(::Float…

One possible reason is just ergonomically defining constructors with all concrete parameters? It gives you access to the constructor you need within the function obviously. If parameters are added you don’t need to worry about changing constructor signatures.

The in-development version of the Manual mentions this: Constructors are just callable objects . This was the PR: doc: manual: constructors: note the correspondence with callable objs by nsajko · Pull Request #53051 · JuliaLang/julia · GitHub

Are these type functors the same as Outer Constructors?

General Usage

Oscar_Smith February 22, 2024, 6:53pm 2

No. These are callable structs (see Function factories or callable structs?)

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Are these type functors the same as Outer Constructors?

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