make RNN/LSTM/GRU Cells immutable - FluxML#1089

check that CUDNN drop solves for too many wrappers - FluxML#1259

Author: jeremiedb

src/layers/recurrent.jl

@@ -59,7 +59,7 @@ flip(f, xs) = reverse(f.(reverse(xs)))
 
 # Vanilla RNN
 
-mutable struct RNNCell{F,A,V}
+struct RNNCell{F,A,V}
   σ::F
   Wi::A
   Wh::A
@@ -96,7 +96,7 @@ RNN(a...; ka...) = Recur(RNNCell(a...; ka...))
 
 # LSTM
 
-mutable struct LSTMCell{A,V}
+struct LSTMCell{A,V}
   Wi::A
   Wh::A
   b::V
@@ -141,7 +141,7 @@ LSTM(a...; ka...) = Recur(LSTMCell(a...; ka...))
 
 # GRU
 
-mutable struct GRUCell{A,V}
+struct GRUCell{A,V}
   Wi::A
   Wh::A
   b::V

test/rnn-test-jdb.jl

@@ -3,6 +3,14 @@ using Flux
 # using CUDA
 using Statistics: mean
 
+################################################
+# Too many wrappers issue #1259
+################################################
+m = RNN(3,2) |> gpu
+x = CUDA.ones(3,2)
+gs = gradient(() -> sum(m(x)), params(m))
+gs[m.cell.Wi]
+
 ########################
 # RNN test gpu
 ########################