Make empty Size() type stable (#28)

* Make empty Size() type stable

* Bump version

Author: jipolanco

Project.toml

@@ -1,6 +1,6 @@
 name = "StaticArraysCore"
 uuid = "1e83bf80-4336-4d27-bf5d-d5a4f845583c"
-version = "1.4.2"
+version = "1.4.3"
 
 [compat]
 julia = "1.6"

src/StaticArraysCore.jl

@@ -491,6 +491,7 @@ end
 
 Base.@pure Size(s::Tuple{Vararg{StaticDimension}}) = Size{s}()
 Base.@pure Size(s::StaticDimension...) = Size{s}()
+Size() = Size(())
 Size(::Type{T}) where {T<:Tuple} = Size{tuple_tuple(T)}()
 
 Base.show(io::IO, ::Size{S}) where {S} = print(io, "Size", S)

test/runtests.jl

@@ -29,6 +29,7 @@ end
 @testset "Size" begin
     M = SArray{Tuple{2,3,4},Int,3}(tuple(rand(Int, 24)...))
     @test (@inferred Size(M)) === Size(2, 3, 4)
+    @test (@inferred Size()) === Size{()}()
     Ms = Size(M)
     @test repr(Ms) == "Size(2, 3, 4)"
     @test Size(2, StaticArraysCore.Dynamic(), 5) === Size{(2, StaticArraysCore.Dynamic(), 5)}()