From 3215d88a91214bc6bbed75cf21cf1a4a28b0bbfb Mon Sep 17 00:00:00 2001
From: Michael Marshall <43034299+mmphys@users.noreply.github.com>
Date: Wed, 3 Feb 2021 15:17:03 +0000
Subject: [PATCH] Simplify syntax with Grid::EnableIf post code review. Updated
 EnableIf so that ReturnType defaults to void in same way as std::enable_if
 see https://en.cppreference.com/w/cpp/types/enable_if

---
 Grid/lattice/Lattice_transfer.h | 9 +++------
 Grid/simd/Grid_vector_types.h   | 4 ++--
 2 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/Grid/lattice/Lattice_transfer.h b/Grid/lattice/Lattice_transfer.h
index c91fa4d1..5a26cce9 100644
--- a/Grid/lattice/Lattice_transfer.h
+++ b/Grid/lattice/Lattice_transfer.h
@@ -98,8 +98,7 @@ accelerator_inline void convertType(ComplexF & out, const std::complex<float> &
 }
 
 template<typename T>
-accelerator_inline typename std::enable_if<isGridFundamental<T>::value>::type
-convertType(T & out, const T & in) {
+accelerator_inline EnableIf<isGridFundamental<T>> convertType(T & out, const T & in) {
   out = in;
 }
 
@@ -138,14 +137,12 @@ accelerator_inline void convertType(iScalar<T1> & out, const iScalar<T2> & in) {
 }
 
 template<typename T1,typename T2>
-accelerator_inline typename std::enable_if<!isGridScalar<T1>::value>::type
-convertType(T1 & out, const iScalar<T2> & in) {
+accelerator_inline NotEnableIf<isGridScalar<T1>> convertType(T1 & out, const iScalar<T2> & in) {
   convertType(out,in._internal);
 }
 
 template<typename T1,typename T2>
-accelerator_inline typename std::enable_if<!isGridScalar<T2>::value>::type
-convertType(iScalar<T1> & out, const T2 & in) {
+accelerator_inline NotEnableIf<isGridScalar<T2>> convertType(iScalar<T1> & out, const T2 & in) {
   convertType(out._internal,in);
 }
 
diff --git a/Grid/simd/Grid_vector_types.h b/Grid/simd/Grid_vector_types.h
index c07077a3..4f952bb2 100644
--- a/Grid/simd/Grid_vector_types.h
+++ b/Grid/simd/Grid_vector_types.h
@@ -208,8 +208,8 @@ struct RealPart<complex<T> > {
 //////////////////////////////////////
 // type alias used to simplify the syntax of std::enable_if
 template <typename T> using Invoke = typename T::type;
-template <typename Condition, typename ReturnType> using EnableIf    = Invoke<std::enable_if<Condition::value, ReturnType> >;
-template <typename Condition, typename ReturnType> using NotEnableIf = Invoke<std::enable_if<!Condition::value, ReturnType> >;
+template <typename Condition, typename ReturnType = void> using EnableIf    = Invoke<std::enable_if<Condition::value, ReturnType> >;
+template <typename Condition, typename ReturnType = void> using NotEnableIf = Invoke<std::enable_if<!Condition::value, ReturnType> >;
 
 ////////////////////////////////////////////////////////
 // Check for complexity with type traits