Unpirate Union{}[] (#685)

* Duplicate SA[] function signatures to avoid Union{} special case
* Test that Union{}[] and friends don't hit the StaticArrays code paths

Co-Authored-By: Chris Foster <chris42f@gmail.com>

src/initializers.jl

@@ -26,9 +26,16 @@ const SA_F64 = SA{Float64}
 @inline similar_type(::Type{SA}, ::Size{S}) where {S} = SArray{Tuple{S...}}
 @inline similar_type(::Type{SA{T}}, ::Size{S}) where {T,S} = SArray{Tuple{S...}, T}
 
-@inline Base.getindex(sa::Type{<:SA}, xs...) = similar_type(sa, Size(length(xs)))(xs)
-@inline Base.typed_vcat(sa::Type{<:SA}, xs::Number...) = similar_type(sa, Size(length(xs)))(xs)
-@inline Base.typed_hcat(sa::Type{<:SA}, xs::Number...) = similar_type(sa, Size(1,length(xs)))(xs)
+# These definitions are duplicated to avoid matching `sa === Union{}` in the
+# neater-looking alternative `sa::Type{<:SA}`.
+@inline Base.getindex(sa::Type{SA}, xs...)            = similar_type(sa, Size(length(xs)))(xs)
+@inline Base.getindex(sa::Type{SA{T}}, xs...) where T = similar_type(sa, Size(length(xs)))(xs)
+
+@inline Base.typed_vcat(sa::Type{SA}, xs::Number...)            = similar_type(sa, Size(length(xs)))(xs)
+@inline Base.typed_vcat(sa::Type{SA{T}}, xs::Number...) where T = similar_type(sa, Size(length(xs)))(xs)
+
+@inline Base.typed_hcat(sa::Type{SA}, xs::Number...)            = similar_type(sa, Size(1,length(xs)))(xs)
+@inline Base.typed_hcat(sa::Type{SA{T}}, xs::Number...) where T = similar_type(sa, Size(1,length(xs)))(xs)
 
 Base.@pure function _SA_hvcat_transposed_size(rows)
     M = rows[1]
@@ -40,7 +47,7 @@ Base.@pure function _SA_hvcat_transposed_size(rows)
     Size(M, length(rows))
 end
 
-@inline function Base.typed_hvcat(sa::Type{<:SA}, rows::Dims, xs::Number...)
+@inline function _SA_typed_hvcat(sa, rows, xs)
     msize = _SA_hvcat_transposed_size(rows)
     if msize === nothing
         throw(ArgumentError("SA[...] matrix rows of length $rows are inconsistent"))
@@ -49,3 +56,6 @@ end
     transpose(similar_type(sa, msize)(xs))
 end
 
+@inline Base.typed_hvcat(sa::Type{SA}, rows::Dims, xs::Number...)            = _SA_typed_hvcat(sa, rows, xs)
+@inline Base.typed_hvcat(sa::Type{SA{T}}, rows::Dims, xs::Number...) where T = _SA_typed_hvcat(sa, rows, xs)
+

test/initializers.jl

@@ -36,4 +36,14 @@ SA_test_hvcat(x,T) = SA{T}[1 x x;
 @test SA_F64[1, 2] === SVector{2,Float64}((1,2))
 @test SA_F32[1, 2] === SVector{2,Float32}((1,2))
 
+# https://github.com/JuliaArrays/StaticArrays.jl/pull/685
+@test Union{}[] isa Vector{Union{}}
+@test Base.typed_vcat(Union{}) isa Vector{Union{}}
+@test Base.typed_hcat(Union{}) isa Vector{Union{}}
+@test Base.typed_hvcat(Union{}, ()) isa Vector{Union{}}
+@test_throws MethodError Union{}[1]
+@test_throws MethodError Union{}[1 2]
+@test_throws MethodError Union{}[1; 2]
+@test_throws MethodError Union{}[1 2; 3 4]
+
 end