constructing a FixedSizeArray from a generator

[nsajko]

Regular Arrays can be conveniently constructed using comprehensions:

julia> [(i, j) for i=1:3, j=1:2]
3×2 Matrix{Tuple{Int64, Int64}}:
 (1, 1)  (1, 2)
 (2, 1)  (2, 2)
 (3, 1)  (3, 2)

The above is basically equivalent to constructing a generator and collecting it:

julia> collect((i, j) for i=1:3, j=1:2)
3×2 Matrix{Tuple{Int64, Int64}}:
 (1, 1)  (1, 2)
 (2, 1)  (2, 2)
 (3, 1)  (3, 2)

A proposal exists to have Array constructors behave equivalently to collect here: JuliaLang/julia#16029. We do need some nice way of constructing FixedSizeArrays, so maybe we could have a constructor method that takes a Base.Generator? Or at least a convert method.

[nsajko]

A related issue is that constructing FixedSizeArrays from iterators could be more convenient if we could use Julia's type inference, and some packages do use Core.Compiler.return_type, but this is currently not permitted. Perhaps an issue should be created on JuliaLang/julia to try and get an interface for type inference.

[nsajko]

xref JuliaLang/julia#54207