Merge pull request #739 from JuliaDiff/ox/getfield

add frules for getfield

Author: oxinabox

src/rulesets/Base/indexing.jl

@@ -1,6 +1,10 @@
 # Int rather than Int64/Integer is intentional
-function frule((_, ẋ), ::typeof(getfield), x::Tuple, i::Int)
-    return x.i, ẋ.i
+function ChainRulesCore.frule((_, Δ, _), ::typeof(getfield), strct, sym::Union{Int,Symbol})
+    return (getfield(strct, sym), isa(Δ, NoTangent) ? NoTangent() : getproperty(Δ, sym))
+end
+
+function ChainRulesCore.frule((_, Δ, _, _), ::typeof(getfield), strct, sym::Union{Int,Symbol}, inbounds)
+    return (getfield(strct, sym, inbounds), isa(Δ, NoTangent) ? NoTangent() : getproperty(Δ, sym))
 end
 
 "for a given tuple type, returns a Val{N} where N is the length of the tuple"

test/rulesets/Base/indexing.jl

@@ -1,3 +1,19 @@
+struct FooTwoField
+    x::Float64
+    y::Float64
+end
+ 
+
+@testset "getfield" begin
+   test_frule(getfield, FooTwoField(1.5, 2.5), :x, check_inferred=false)
+    
+    test_frule(getfield, (; a=1.5, b=2.5), :a, check_inferred=false)
+    test_frule(getfield, (; a=1.5, b=2.5), 2)
+
+    test_frule(getfield, (1.5, 2.5), 2)
+    test_frule(getfield, (1.5, 2.5), 2, true)
+end
+
 @testset "getindex" begin
     @testset "getindex(::Tuple, ...)" begin
         x = (1.2, 3.4, 5.6)