From 782fc9650cde202a9b26bf32dd9f8892f391f6ce Mon Sep 17 00:00:00 2001
From: Alex Arslan <ararslan@comcast.net>
Date: Fri, 22 Mar 2019 10:47:24 -0700
Subject: [PATCH] Add sensitivities for float (#143)

`float` acts on arrays and scalars, turning integers into floats of the
corresponding size (e.g. `float(::Int32)` -> `Float32`) and is a no-op
for floats. This same behavior is applied when differentiating.
---
 src/sensitivities/scalar.jl  |  4 ++++
 test/sensitivities/scalar.jl | 20 ++++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/src/sensitivities/scalar.jl b/src/sensitivities/scalar.jl
index 1ea7ae75..531854b6 100644
--- a/src/sensitivities/scalar.jl
+++ b/src/sensitivities/scalar.jl
@@ -44,3 +44,7 @@ end
 
 # Add method to resolve exponentiation ambiguity.
 ^(n::Node{<:Real}, p::Integer) = invoke(^, Tuple{Node{<:Real}, Real}, n, p)
+
+import Base: float
+@explicit_intercepts float Tuple{∇ArrayOrScalar}
+∇(::typeof(float), ::Type{Arg{1}}, p, y, ȳ, x) = float(ȳ)
diff --git a/test/sensitivities/scalar.jl b/test/sensitivities/scalar.jl
index 214cdd45..b1f6d0a5 100644
--- a/test/sensitivities/scalar.jl
+++ b/test/sensitivities/scalar.jl
@@ -91,4 +91,24 @@ end
         # Test whether the exponentiation amibiguity is resolved.
         @test ∇(x -> x^2)(1) == (2.0,)
     end
+
+    @testset "float" begin
+        # Scalars
+        x_ = 4
+        x = Leaf(Tape(), x_)
+        y = float(x)
+        @test y isa Branch{Float64}
+        @test unbox(y) == 4.0
+
+        # Arrays
+        X_ = [1,2,3,4]
+        X = Leaf(Tape(), X_)
+        Y = float(X)
+        @test Y isa Branch{Vector{Float64}}
+        @test unbox(Y) == Float64[1,2,3,4]
+
+        # In expressions
+        @test ∇(x->2x)(1) === (2,)
+        @test ∇(x->2*float(x))(1) === (2.0,)
+    end
 end