From 8e59160df6e8126282d251379f421e84e0021d86 Mon Sep 17 00:00:00 2001
From: Mike J Innes <mike.j.innes@gmail.com>
Date: Sun, 20 Aug 2017 13:35:20 +0100
Subject: [PATCH] inferable broadcast

---
 src/Tracker/lib.jl | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/Tracker/lib.jl b/src/Tracker/lib.jl
index 55a1cdaf..0e8c573f 100644
--- a/src/Tracker/lib.jl
+++ b/src/Tracker/lib.jl
@@ -33,8 +33,11 @@ dualify(xs, n) = xs
 dualify(xs::TrackedArray, ps) = Dual.(data(xs), Ref(ps))
 
 function tracked_broadcast(f, args::Vararg{Any,N}) where N
-  dargs = ntuple(i -> dualify(args[i], ntuple(j -> i==j, Val{N})), Val{N})
-  TrackedArray(Call(Broadcasted(broadcast(f, dargs...)), args...))
+  dargs = map((x,i) -> dualify(x, ntuple(j -> i==j, Val{N})), args, ntuple(identity, Val{N}))
+  # TrackedArray(Call(Broadcasted(broadcast(f, dargs...)), args...))
+  # Works around a 0.6 type inference issue
+  b = Broadcasted(broadcast(f, dargs...))
+  TrackedArray(Call(b, args...), b())
 end
 
 function back!(b::Broadcasted, Δ, args...)