Implement read() write() and read!() for static arrays

Unfortunately these allocate, but there doesn't seem to be a way to
avoid this yet, until the compiler can allocate Base.RefValue on the
stack (even Base.read(io, Float64) allocates!)

Author: Chris Foster

src/StaticArrays.jl

@@ -11,7 +11,7 @@ import Base: getindex, setindex!, size, similar, vec, show,
              fill!, det, inv, eig, eigvals, trace, vecnorm, norm, dot, diagm,
              sum, diff, prod, count, any, all, sumabs, sumabs2, minimum,
              maximum, extrema, mean, copy, rand, randn, randexp, rand!, randn!,
-             randexp!, normalize, normalize!
+             randexp!, normalize, normalize!, read, read!, write
 
 export StaticScalar, StaticArray, StaticVector, StaticMatrix
 export Scalar, SArray, SVector, SMatrix
@@ -92,6 +92,7 @@ include("solve.jl")
 include("eigen.jl")
 include("cholesky.jl")
 include("deque.jl")
+include("io.jl")
 
 include("FixedSizeArrays.jl")
 include("ImmutableArrays.jl")

src/io.jl

@@ -0,0 +1,18 @@
+
+@inline function read(io::IO, ::Type{SA}) where {SA<:StaticArray}
+    # Copy Base implementation of `read` for primitive types.  This is less
+    # efficient in 0.6 that we'd like because creating the Ref allocates.
+    elements = Ref{NTuple{length(SA),eltype(SA)}}()
+    read(io, elements)
+    SA(elements[])
+end
+
+@inline function read!(io::IO, a::SA) where {SA<:StaticArray}
+    unsafe_read(io, Base.unsafe_convert(Ptr{eltype(SA)}, a), sizeof(a))
+    a
+end
+
+@inline function write(io::IO, a::SA) where {SA<:StaticArray}
+    write(io, Ref(Tuple(a)))
+end
+

test/io.jl

@@ -0,0 +1,37 @@
+# Serialize `xs` as type `T` to an IOBuffer one by one using Base.write.
+# Return the buffer positioned at the start, ready for reading
+write_buf(::Type{T}, xs...) where {T} = write_buf(map(T, xs)...)
+
+function write_buf(xs...)
+    io = IOBuffer()
+    foreach(x->write(io, x), xs)
+    seek(io, 0)
+    io
+end
+
+@testset "Binary IO" begin
+    @testset "read" begin
+        # Read static arrays from a stream which was serialized elementwise
+        @test read(write_buf(UInt8, 1,2,3), SVector{3,UInt8})         === SVector{3,UInt8}(1,2,3)
+        @test read(write_buf(Int32, -1,2,3), SVector{3,Int32})        === SVector{3,Int32}(-1,2,3)
+        @test read(write_buf(Float64, 1,2,3), SVector{3,Float64})     === SVector{3,Float64}(1,2,3)
+        @test read(write_buf(Float64, 1,2,3,4), SMatrix{2,2,Float64}) === @SMatrix [1.0 3.0; 2.0 4.0]
+    end
+
+    @testset "write" begin
+        # Compare serialized bytes
+        @test take!(write_buf(UInt8, 1,2,3))     == take!(write_buf(SVector{3,UInt8}(1,2,3)))
+        @test take!(write_buf(Int32, -1,2,3))    == take!(write_buf(SVector{3,Int32}(-1,2,3)))
+        @test take!(write_buf(Float64, 1,2,3))   == take!(write_buf(SVector{3,Float64}(1,2,3)))
+        @test take!(write_buf(Float64, 1,2,3,4)) == take!(write_buf(@SMatrix [1.0 3.0; 2.0 4.0]))
+    end
+
+    @testset "read!" begin
+        # Read static arrays from a stream which was serialized elementwise
+        @test read!(write_buf(UInt8, 1,2,3),     zeros(MVector{3,UInt8}))     == MVector{3,UInt8}(1,2,3)
+        @test read!(write_buf(Int32, -1,2,3),    zeros(MVector{3,Int32}))     == MVector{3,Int32}(-1,2,3)
+        @test read!(write_buf(Float64, 1,2,3),   zeros(MVector{3,Float64}))   == MVector{3,Float64}(1,2,3)
+        @test read!(write_buf(Float64, 1,2,3,4), zeros(MMatrix{2,2,Float64})) == @MMatrix [1.0 3.0; 2.0 4.0]
+    end
+end
+

test/runtests.jl

@@ -26,5 +26,7 @@ using Base.Test
     include("solve.jl") # Strange inference / world-age error
     include("eigen.jl")
     include("deque.jl")
+    include("io.jl")
+
     include("fixed_size_arrays.jl")
 end