Fully FieldVector Broadcasts Drop Names

[ChrisRackauckas]

Using #313 for simplicity:

a = @FVector Float64 [a,b,c] [1,2,3]
b = a.+a
c = @MFVector Float64 [a,b,c] [1,2,3]
d = c.+c

The type of b here is SVector and the type of d here is SVector as well. It would be nice if in this case where the types are all known to be the same FieldVector that it can stay that FieldVector so that the return type has the same naming.

[andyferris]

You need to overload similar_type. Please note that you have exactly the same behavior in standard (non static) AbstractArrays except in Base you need to overload similar, in order to get an array of the same type out of methods in Base.

[ChrisRackauckas]

Should this be done on the abstract type so that way by default this works properly?

[ChrisRackauckas]

Overloading similar_type didn't work.

StaticArrays.similar_type(a::T) where T<:FieldVector = T
similar_type(a) # ##FVector#661
b = a.+a

3-element SVector{3,Float64}:
 2.0
 4.0
 6.0

[andyferris]

Oh, sorry, the docs aren't clear enough here! For 3 vectors, please overload:

similar_type(::Type{<:MyFieldVector}, ::Type{T}, ::Size{(3,)}) where {T} = MyFieldVector{T}

The 3-argument form is what gets used in practice.

You can't overload all of FieldVector since (a) sometimes you need a matrix or different sized vector, so that won't work, and (b) some users may wish to implement a custom type which has special properties (I'm thinking Rotations.jl which has orthogonal matrices) and thus should fall back to SVector when arbitrary transformations occur.

[andyferris]

Should this be done on the abstract type so that way by default this works properly?

To follow up, we copy the pattern from Base where things fall back to Array unless otherwise specified. (Generally, we also aim to follow the design of Base as closely as possible, and in this case I think this has been considered and came to the same conclusions as I mention above).

[andyferris]

Did overloading that method work for you?

[ChrisRackauckas]

It worked