support empty tuples and named tuples

Author: piever

src/to_vec.jl

@@ -227,6 +227,14 @@ end
 
 # Non-array data structures
 
+function to_vec(::Tuple{})
+    vec = Bool[]
+    function Tuple_from_vec(_)
+        return ()
+    end
+    return vec, Tuple_from_vec
+end
+
 function to_vec(x::Tuple)
     x_vecs_and_backs = map(to_vec, x)
     x_vecs, x_backs = first.(x_vecs_and_backs), last.(x_vecs_and_backs)

test/to_vec.jl

@@ -226,6 +226,12 @@ end
                 x_comp = Tangent{typeof(x_outer)}(1, Tangent{typeof(x_inner)}(2, 3))
                 test_to_vec(x_comp; check_inferred=false)
             end
+
+            @testset "empty" begin
+                x_tup = ()
+                x_comp = Tangent{typeof(x_tup)}(x_tup...)
+                test_to_vec(x_comp)
+            end
         end
 
         @testset "Tangent Struct" begin
@@ -235,6 +241,12 @@ end
                 test_to_vec(comp)
             end
 
+            @testset "NamedTuple empty" begin
+                nt = NamedTuple()
+                comp = Tangent{typeof(nt)}(; nt...)
+                test_to_vec(comp)
+            end
+
             @testset "Struct" begin
                 test_to_vec(Tangent{ThreeFields}(; a=10.0, b=20.0, c=30.0))
                 test_to_vec(Tangent{ThreeFields}(; a=10.0, b=20.0,)) # broken on Julia 1.6.0, fixed on 1.6.1