Type changes from MArray to SArray upon using broadcast (vectorization)

[eeshan9815]

julia> a = @MMatrix randn(2, 2)
2×2 StaticArrays.MArray{Tuple{2,2},Float64,2,4}:
 1.16721   -1.01285
 0.221507   0.00572563

julia> sa = sin.(a)
2×2 StaticArrays.SArray{Tuple{2,2},Float64,2,4}:
 0.919658  -0.848346
 0.2197     0.0057256

Why is sa of the type SArray whereas a is of the type MArray?

[tkoolen]

(Note: just a contributor). I think the current convention is to avoid allocation whenever possible.
There's something to be said for either option, see also

StaticArrays.jl/src/abstractarray.jl

Lines 60 to 61 in 8e36860

	# should mutable things stay mutable?
	#similar_type{SA<:Union{MVector,MMatrix,MArray},T,S}(::Type{SA},::Type{T},s::Size{S}) = mutable_similar_type(T,s,length_val(s))

but I think the current behavior would be frequently desirable (what with StaticArrays being all about getting the best performance possible).

Note that you can always do

julia> a = @MMatrix randn(2, 2)
2×2 StaticArrays.MArray{Tuple{2,2},Float64,2,4}:                                                                                                                                                                                                                                
 -0.266148  -0.146905                                                                                                                                                                                                                                                           
  0.67229    1.57561                                                                                                                                                                                                                                                            
                                                                                                                                                                                                                                                                                
julia> sa = MMatrix{2, 2, Float64}()
2×2 StaticArrays.MArray{Tuple{2,2},Float64,2,4}:                                                                                                                                                                                                                                
 1.4822e-323  6.9015e-310                                                                                                                                                                                                                                                       
 6.9015e-310  0.0        

julia> sa .= sin.(a)
2×2 StaticArrays.MArray{Tuple{2,2},Float64,2,4}:
 -0.263017  -0.146378
  0.622779   0.999988

There would not be an easy workaround like the one above if an MArray were returned by default and you wanted an SArray without allocating.

[andyferris]

See also #327

[c42f]

Was solved in #536, which I'm now fairly confident was the right choice :-)