Conversion to Static arrays

[jw3126]

Currently there is no conversion from Base Arrays to static arrays:

julia> using StaticArrays

julia> SVector([1,2,3])
ERROR: MethodError: no method matching size(::Type{StaticArrays.SVector})
Closest candidates are:
  size{T<:StaticArrays.StaticArray{T,N}}(::Union{T<:StaticArrays.StaticArray{T,N},Type{T<:StaticArrays.StaticArray}}, ::Integer) at /home/admin/.julia/v0.5/StaticArrays/src/abstractarray.jl:4
  size{N}(::Any, ::Integer, ::Integer, ::Integer...) at abstractarray.jl:48
  size(::BitArray{1}) at bitarray.jl:39
  ...
 in StaticArrays.SVector{S,T}(::Array{Int64,1}) at ./sysimg.jl:53

Is there a good reason not to have such conversion?

[c42f]

This is unimplemented because it work would lead to a performance trap - the output shape (and hence type) of SVector{A<:AbstractArray}(a::A) cannot be inferred in general. See #31 for discussion.

[andyferris]

Is this covered in the read me? Might be a good idea.

@jw3126 try SVector{3}([1,2,3]). Don't think of a static array type as a complete type until its size is specified or is inferrable.

[jw3126]

Yeah, I understand the type instability trap. I was porting some code from FixedSizeArrays to StaticArrays and having this conversion gone broke some of my tests.
I agree its reasonable design for StaticArrays to make it inconvenient writing slow code. Btw StaticArrays is really awesome!

[c42f]

Is this covered in the read me?

Is now: https://github.com/JuliaArrays/StaticArrays.jl#conversions-from-array

[andyferris]

Thanks Chris; looks good. :)

[andyferris]

There are now also docstrings and the "quick start" part of the README explaining this, as well as a decent error message. Hopefully this will reduce the volume of this request somewhat.

[c42f]

Nice @andyferris, this is a lot better.