arrays of arrays

src/destructure.jl

@@ -102,7 +102,12 @@ function _Tangent_biwalk(f, x, aux)  # use with prune = NoT
   au, _ = functor(typeof(x), aux)
   y = _trainmap(f, ch, _trainable(x), au)
   y isa Tuple{} && return NoT
-  Tangent{typeof(x), typeof(y)}(y)
+  p = ProjectTo(x)
+  if p isa ProjectTo  # e.g. Array, NamedTuple
+    p(y)
+  else  # p === identity for unknown structs
+    Tangent{typeof(x), typeof(y)}(y)
+  end
 end
 
 function ChainRulesCore.rrule(::typeof(_rebuild), x, off, flat, len; kw...)

src/interface.jl

@@ -71,6 +71,7 @@ trainable(x) = functor(x)[1]
 _trainable(x) = _trainable(functor(x)[1], trainable(x))
 _trainable(ch::NamedTuple, tr::NamedTuple) = merge(map(_ -> nothing, ch), tr)
 _trainable(ch::Tuple{Vararg{Any,N}}, tr::Tuple{Vararg{Any,N}}) where N = tr
+_trainable(ch::AbstractArray, tr::AbstractArray) = tr
 function _trainable(ch::NamedTuple, tr::Tuple)  # for old Flux-style no-names tuple
   @warn "trainable(x) should now return a NamedTuple with the field names, not a Tuple"
   map(c -> c in tr ? c : nothing, ch)

test/destructure.jl

@@ -6,6 +6,7 @@ m4 = (x = m1, y = m1, z = collect(4:6.0))
 m5 = (a = (m3, true), b = (m1, false), c = (m4, true))
 m6 = (a = m1, b = [4.0 + im], c = m1)
 m7 = TwoThirds((sin, collect(1:3.0)), (cos, collect(4:6.0)), (tan, collect(7:9.0)))
+m8 = [Foo(m1, m1), (a = true, b = Foo([4.0], false), c = ()), [[5.0]]]
 
 @testset "flatten & rebuild" begin
   @test destructure(m1)[1] isa Vector{Float64}
@@ -31,12 +32,20 @@ m7 = TwoThirds((sin, collect(1:3.0)), (cos, collect(4:6.0)), (tan, collect(7:9.0
   @test m6′.a === m6′.c
   @test m6′.b == [7 + 4im]
 
+  # struct, trainable
   @test destructure(m7)[1] == 1:3
   m7′ = destructure(m7)[2]([10,20,30])
   @test m7′.a == (sin, [10,20,30])
   @test m7′.b == (cos, [4,5,6])
   @test m7′.c == (tan, [7,8,9])
 
+  @test destructure(m8)[1] == 1:5
+  m8′ = destructure(m8)[2](1:5)
+  @test m8′[1].x === m8′[1].y
+  @test m8′[2].b.y === false
+  @test m8′[3][1] == [5.0]
+
+  # errors
   @test_throws Exception destructure(m7)[2]([10,20])
   @test_throws Exception destructure(m7)[2]([10,20,30,40])
 end
@@ -57,6 +66,11 @@ end
   @test g6.a isa Vector{Float64}
   @test g6.b == [0+im]
 
+  g8 = gradient(m -> sum(abs2, destructure(m)[1]), m8)[1]
+  @test g8[1].x == [2,4,6]
+  @test g8[2].b.x == [8]
+  @test g8[3] == [[10.0]]
+
   @testset "second derivative" begin
     @test_broken gradient([1,2,3.0]) do v
       sum(abs2, gradient(m -> sum(abs2, destructure(m)[1]), (v, [4,5,6.0]))[1][1])
@@ -90,6 +104,10 @@ end
   @test gradient(x -> re7(x).b[2][2], rand(3))[1] == [0,0,0]
   @test gradient(x -> re7(x).c[2][1], rand(3))[1] == [0,0,0]
 
+  v8, re8 = destructure(m8)
+  @test gradient(x -> sum(abs2, re8(x)[1].y), v8)[1] == [2,4,6,0,0]
+  @test gradient(x -> only(sum(re8(x)[3]))^2, v8)[1] == [0,0,0,0,10]
+
   @testset "second derivative" begin
     # ERROR: Need an adjoint for constructor ChainRulesCore.Tangent{Any, Tuple{Vector{Float64}, ChainRulesCore.ZeroTangent}}. Gradient is of type Tuple{Vector{Float64}, Vector{Float64}}
     @test_broken gradient(collect(1:6.0)) do y