Merge pull request #425 from JuliaDiff/mz/base

`view` and `sum` for `AbstractZero`s

Author: mzgubic

Project.toml

@@ -1,6 +1,6 @@
 name = "ChainRulesCore"
 uuid = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
-version = "1.2.0"
+version = "1.3.0"
 
 [deps]
 Compat = "34da2185-b29b-5c13-b0c7-acf172513d20"

src/differentials/abstract_zero.jl

@@ -28,6 +28,9 @@ Base.convert(::Type{T}, x::AbstractZero) where T <: Number = zero(T)
 
 Base.getindex(z::AbstractZero, k) = z
 
+Base.view(z::AbstractZero, ind...) = z
+Base.sum(z::AbstractZero; dims=:) = z
+
 """
     ZeroTangent() <: AbstractZero
 

test/differentials/abstract_zero.jl

@@ -4,6 +4,14 @@
         @test iszero(NoTangent())
     end
 
+    @testset "Linear operators" begin
+        @test view(ZeroTangent(), 1) == ZeroTangent()
+        @test view(NoTangent(), 1, 2) == NoTangent()
+
+        @test sum(ZeroTangent()) == ZeroTangent()
+        @test sum(NoTangent(); dims=2) == NoTangent()
+    end
+
     @testset "ZeroTangent" begin
         z = ZeroTangent()
         @test z + z === z