From f1d98d6bd543b90d9b85fe2e4e40cae3e2e6b69a Mon Sep 17 00:00:00 2001
From: Nicolas Clauvelin <nclauvelin@sendyne.com>
Date: Sun, 11 Mar 2018 17:34:38 -0400
Subject: [PATCH] REVISED SHADOW VALUE USING INTEGRAL CONSTANT

This provides a clearer interface compared to defining a constexpr bool member.
---
 register/Field.h       |  6 +++---
 register/MergeWrite.h  |  4 ++--
 register/ShadowValue.h | 14 ++++----------
 3 files changed, 9 insertions(+), 15 deletions(-)

diff --git a/register/Field.h b/register/Field.h
index 44082ce..06fd33f 100644
--- a/register/Field.h
+++ b/register/Field.h
@@ -69,7 +69,7 @@ namespace cppreg {
 
         //! Boolean flag indicating if a shadow value is used.
         constexpr static const bool has_shadow =
-            parent_register::shadow::use_shadow;
+            parent_register::shadow::value;
 
         //! Customized overflow check implementation for Field types.
         /**
@@ -124,13 +124,13 @@ namespace cppreg {
             // Update shadow value.
             // This assumes that reading a write-only fields return some value.
             RegisterWrite<type, type, mask, offset>
-            ::write(&parent_register::shadow::value, value);
+            ::write(&parent_register::shadow::shadow_value, value);
 
             // Write as a block to the register, that is, we do not use the
             // mask and offset.
             policy::template write<MMIO_t, type, type_mask<type>::value, 0u>(
                 parent_register::rw_mem_pointer(),
-                parent_register::shadow::value
+                parent_register::shadow::shadow_value
                                                                             );
 
         };
diff --git a/register/MergeWrite.h b/register/MergeWrite.h
index 64171ca..0e4ed35 100644
--- a/register/MergeWrite.h
+++ b/register/MergeWrite.h
@@ -60,7 +60,7 @@ namespace cppreg {
     private:
 
         // Disabled for shadow value register.
-        static_assert(!Register::shadow::use_shadow,
+        static_assert(!Register::shadow::value,
                       "merge write is not available for shadow value register");
 
         // Accumulated value.
@@ -245,7 +245,7 @@ namespace cppreg {
     private:
 
         // Disabled for shadow value register.
-        static_assert(!Register::shadow::use_shadow,
+        static_assert(!Register::shadow::value,
                       "merge write is not available for shadow value register");
 
         // Private default constructor.
diff --git a/register/ShadowValue.h b/register/ShadowValue.h
index 1328671..e145787 100644
--- a/register/ShadowValue.h
+++ b/register/ShadowValue.h
@@ -24,10 +24,7 @@ namespace cppreg {
      *
      * This implementation is for register which do not require shadow value.
      */
-    template <typename Register, bool UseShadow>
-    struct Shadow {
-        constexpr static const bool use_shadow = false;
-    };
+    template <typename Register, bool UseShadow> struct Shadow : std::false_type {};
 
 
     //! Shadow value implementation.
@@ -39,15 +36,12 @@ namespace cppreg {
      * See 
      */
     template <typename Register>
-    struct Shadow<Register, true> {
-        static typename Register::type value;
-        constexpr static const bool use_shadow = true;
+    struct Shadow<Register, true> : std::true_type {
+        static typename Register::type shadow_value;
     };
     template <typename Register>
-    typename Register::type Shadow<Register, true>::value =
+    typename Register::type Shadow<Register, true>::shadow_value =
         Register::reset;
-    template <typename Register>
-    constexpr const bool Shadow<Register, true>::use_shadow;
 
 
 }