fix: reducing over empty collection

Project.toml

@@ -1,7 +1,7 @@
 name = "Functors"
 uuid = "d9f16b24-f501-4c13-a1f2-28368ffc5196"
 authors = ["Mike J Innes <mike.j.innes@gmail.com>"]
-version = "0.4.11"
+version = "0.4.12"
 
 [deps]
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"

src/walks.jl

@@ -315,6 +315,6 @@ function (walk::FlattenWalk)(recurse, x, ys...)
   x_children = _values(children(x))
   ys_children = map(children, ys)
   res = _map(recurse, x_children, ys_children...)
-  return reduce(vcat, _values(res))
+  return reduce(vcat, _values(res); init = [])
 end
 

test/basics.jl

@@ -439,6 +439,9 @@ end
   @test xflat isa Vector
   @test length(xflat) == 3
   @test 1 ∈ xflat && 2 ∈ xflat && [1, 2, 3] ∈ xflat
+
+  @test fleaves((;)) == []
+  @test fleaves((; a = 1, b = 2, c = (;))) == [1, 2]
 end
 
 @testset "fmap_with_path" begin