namedtuple getfield, for iteration

Co-Authored-By: dhairyagandhi96 <dhairya@juliacomputing.com>

Author: MikeInnes

src/lib/lib.jl

@@ -105,6 +105,9 @@ end
 @adjoint Core.getfield(xs::NTuple{N,Any}, i::Integer) where N =
   (xs[i], Δ -> (ntuple(j -> i == j ? Δ : nothing, Val(N)), nothing))
 
+@adjoint Core.getfield(xs::NamedTuple{K,<:NTuple{N,Any}}, i::Integer) where {K,N} =
+  (xs[i], Δ -> (NamedTuple{K}(ntuple(j -> i == j ? Δ : nothing, Val(N))), nothing))
+
 @adjoint function Base.first(xs::Tuple)
   drest = map(_->nothing, tail(xs))
   first(xs), Δ -> ((Δ, drest...),)