improve type stability of cat (#258)

* improve type stability

* bump version

Co-authored-by: Alexander Plavin <alexander@plav.in>

Project.toml

@@ -1,6 +1,6 @@
 name = "StructArrays"
 uuid = "09ab397b-f2b6-538f-b94a-2f83cf4a842a"
-version = "0.6.13"
+version = "0.6.14"
 
 [deps]
 Adapt = "79e6a3ab-5dfb-504d-930d-738a2a938a0e"

src/structarray.jl

@@ -450,12 +450,13 @@ function Base.sizehint!(s::StructArray, i::Integer)
 end
 
 for op in [:cat, :hcat, :vcat]
+    curried_op = Symbol(:curried, op)
     @eval begin
-        function Base.$op(arg1::StructArray, argsrest::StructArray...; kwargs...)
-            args = (arg1, argsrest...)
-            f = key -> $op((getproperty(t, key) for t in args)...; kwargs...)
+        function Base.$op(arg::StructArray, others::StructArray...; kwargs...)
+            $curried_op(A...) = $op(A...; kwargs...)
+            args = (arg, others...)
             T = mapreduce(eltype, promote_type, args)
-            StructArray{T}(map(f, propertynames(arg1)))
+            StructArray{T}(map($curried_op, map(components, args)...))
         end
     end
 end

test/runtests.jl

@@ -636,8 +636,11 @@ end
     horizontal_concat = StructArray{Pair{Int, String}}(([3 1; 5 6], ["a" "a"; "b" "b"]))
     @test cat(t, t2; dims=2)::StructArray == horizontal_concat == hcat(t, t2)
     @test hcat(t, t2) isa StructArray
-
-    # check that cat(dims=1) doesn't commit type piracy (#254)
+    t3 = StructArray(x=view([1], 1:1:1), y=view([:a], 1:1:1))
+    @test @inferred(vcat(t3)) == t3
+    @inferred vcat(t3, t3)
+    @inferred vcat(t3, collect(t3))
+    # Check that `cat(dims=1)` doesn't commit type piracy (#254)
     # We only test that this works, the return value is immaterial
     @test cat(dims=1) == vcat()
 end