implement some of @oxinabox's suggestions

Author: simeonschaub

src/differentials.jl

@@ -66,9 +66,6 @@ wirtinger_conjugate(::Any) = Zero()
 
 extern(x::AbstractWirtinger) = throw(ArgumentError("`AbstractWirtinger` cannot be converted to an external type."))
 
-Base.iterate(x::AbstractWirtinger) = (x, nothing)
-Base.iterate(::AbstractWirtinger, ::Any) = nothing
-
 # `conj` is not defined for `AbstractWirtinger`.
 # Need this method to override the definition of `conj` for `AbstractDifferential`.
 Base.conj(x::AbstractWirtinger) = throw(MethodError(conj, x))
@@ -102,9 +99,6 @@ wirtinger_conjugate(x::Wirtinger) = x.conjugate
 Base.Broadcast.broadcastable(w::Wirtinger) = Wirtinger(broadcastable(w.primal),
                                                        broadcastable(w.conjugate))
 
-Base.iterate(x::Wirtinger) = (x, nothing)
-Base.iterate(::Wirtinger, ::Any) = nothing
-
 #####
 ##### `ComplexGradient`
 #####

src/rule_definition_tools.jl

@@ -241,15 +241,13 @@ Returns `@thunk body`, except for when `body` is a call to [`Wirtinger`](@ref) o
 In this case, it is equivalent to `Wirtinger(@thunk(primal), @thunk(conjugate))` / `ComplexGradient(@thunk primal)`.
 """
 function _thunk(body)
-    if body isa Expr 
-        if body.head == :call
-            fname = body.args[1]
-            if fname in (:Wirtinger, :ComplexGradient)
-                return :($fname($(thunk_assert_no_wirtinger.(body.args[2:end])...)))
-            end
-        elseif body.head == :escape
-            return Expr(:escape, _thunk(body.args[1]))
+    if Meta.isexpr(body, :call)
+        fname = body.args[1]
+        if fname in (:Wirtinger, :ComplexGradient)
+            return :($fname($(thunk_assert_no_wirtinger.(body.args[2:end])...)))
         end
+    elseif Meta.isexpr(body, :escape)
+        return Expr(:escape, _thunk(body.args[1]))
     end
     return thunk_assert_no_wirtinger(body)
 end

test/differentials.jl

@@ -12,9 +12,6 @@
         # TODO: other + methods stack overflow
         @test_throws ErrorException w*w
         @test_throws ArgumentError extern(w)
-        for x in w
-            @test x === w
-        end
         @test broadcastable(w) == w
         @test_throws MethodError conj(w)
     end