From 3d41dca33871ee1a25e443bfe47d2e5f291091b9 Mon Sep 17 00:00:00 2001
From: Mike J Innes <mike.j.innes@gmail.com>
Date: Fri, 16 Nov 2018 12:22:15 +0000
Subject: [PATCH] immutable chain

---
 src/Flux.jl         |  1 +
 src/layers/basic.jl | 13 ++++++++-----
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/src/Flux.jl b/src/Flux.jl
index 48847fbe..da040aa0 100644
--- a/src/Flux.jl
+++ b/src/Flux.jl
@@ -2,6 +2,7 @@ module Flux
 
 # Zero Flux Given
 
+using Base: tail
 using MacroTools, Juno, Requires, Reexport, Statistics, Random
 using MacroTools: @forward
 
diff --git a/src/layers/basic.jl b/src/layers/basic.jl
index c0188bf2..fddd4fc9 100644
--- a/src/layers/basic.jl
+++ b/src/layers/basic.jl
@@ -16,18 +16,21 @@ m(x) == m[2](m[1](x))
 `Chain` also supports indexing and slicing, e.g. `m[2]` or `m[1:end-1]`.
 `m[1:3](x)` will calculate the output of the first three layers.
 """
-struct Chain
-  layers::Vector{Any}
-  Chain(xs...) = new([xs...])
+struct Chain{T<:Tuple}
+  layers::T
+  Chain(xs...) = new{typeof(xs)}(xs)
 end
 
-@forward Chain.layers Base.getindex, Base.first, Base.last, Base.lastindex, Base.push!
+@forward Chain.layers Base.getindex, Base.first, Base.last, Base.lastindex
 @forward Chain.layers Base.iterate
 
 children(c::Chain) = c.layers
 mapchildren(f, c::Chain) = Chain(f.(c.layers)...)
 
-(c::Chain)(x) = foldl((x, m) -> m(x), c.layers; init = x)
+applychain(::Tuple{}, x) = x
+applychain(fs::Tuple, x) = applychain(tail(fs), first(fs)(x))
+
+(c::Chain)(x) = applychain(c.layers, x)
 
 Base.getindex(c::Chain, i::AbstractArray) = Chain(c.layers[i]...)