message: pack: add variant support

Add variant support to allow return of mutliple specific
types. Also change types to const as this is required by
the visitor and these could have been const all along.

Tested: Added unit test and used in oem provider

Change-Id: I5cb056c15d4813b9eee58eecb707664477d019d9
Signed-off-by: James Feist <james.feist@linux.intel.com>

1 files changed, 24 insertions, 10 deletions

diff --git a/include/ipmid/message/pack.hpp b/include/ipmid/message/pack.hpp
index e6bbbce..104354d 100644
--- a/include/ipmid/message/pack.hpp
+++ b/include/ipmid/message/pack.hpp
@@ -72,7 +72,7 @@ struct PackSingle
      *  @param[in] p - Payload to pack into.
      *  @param[out] t - The reference to pack item into.
      */
-    static int op(Payload& p, T& t)
+    static int op(Payload& p, const T& t)
     {
         // if not on a byte boundary, must pack values LSbit/LSByte first
         if (p.bitCount)
@@ -96,7 +96,7 @@ struct PackSingle
 template <>
 struct PackSingle<std::string>
 {
-    static int op(Payload& p, std::string& t)
+    static int op(Payload& p, const std::string& t)
     {
         // check length first
         uint8_t len;
@@ -118,7 +118,7 @@ struct PackSingle<std::string>
 template <unsigned N>
 struct PackSingle<fixed_uint_t<N>>
 {
-    static int op(Payload& p, fixed_uint_t<N>& t)
+    static int op(Payload& p, const fixed_uint_t<N>& t)
     {
         size_t count = N;
         static_assert(N <= (details::bitStreamSize - CHAR_BIT));
@@ -138,7 +138,7 @@ struct PackSingle<fixed_uint_t<N>>
 template <>
 struct PackSingle<bool>
 {
-    static int op(Payload& p, bool& b)
+    static int op(Payload& p, const bool& b)
     {
         p.appendBits(1, b);
         return 0;
@@ -149,7 +149,7 @@ struct PackSingle<bool>
 template <size_t N>
 struct PackSingle<std::bitset<N>>
 {
-    static int op(Payload& p, std::bitset<N>& t)
+    static int op(Payload& p, const std::bitset<N>& t)
     {
         size_t count = N;
         static_assert(N <= (details::bitStreamSize - CHAR_BIT));
@@ -169,10 +169,10 @@ struct PackSingle<std::bitset<N>>
 template <typename T, size_t N>
 struct PackSingle<std::array<T, N>>
 {
-    static int op(Payload& p, std::array<T, N>& t)
+    static int op(Payload& p, const std::array<T, N>& t)
     {
         int ret = 0;
-        for (auto& v : t)
+        for (const auto& v : t)
         {
             int ret = PackSingle<T>::op(p, v);
             if (ret)
@@ -188,10 +188,10 @@ struct PackSingle<std::array<T, N>>
 template <typename T>
 struct PackSingle<std::vector<T>>
 {
-    static int op(Payload& p, std::vector<T>& t)
+    static int op(Payload& p, const std::vector<T>& t)
     {
         int ret = 0;
-        for (auto& v : t)
+        for (const auto& v : t)
         {
             int ret = PackSingle<T>::op(p, v);
             if (ret)
@@ -207,7 +207,7 @@ struct PackSingle<std::vector<T>>
 template <>
 struct PackSingle<std::vector<uint8_t>>
 {
-    static int op(Payload& p, std::vector<uint8_t>& t)
+    static int op(Payload& p, const std::vector<uint8_t>& t)
     {
         p.raw.reserve(p.raw.size() + t.size());
         p.raw.insert(p.raw.end(), t.begin(), t.end());
@@ -215,6 +215,20 @@ struct PackSingle<std::vector<uint8_t>>
     }
 };
 
+/** @brief Specialization of PackSingle for std::variant<T, N> */
+template <typename... T>
+struct PackSingle<std::variant<T...>>
+{
+    static int op(Payload& p, const std::variant<T...>& v)
+    {
+        return std::visit(
+            [&p](const auto& arg) {
+                return PackSingle<std::decay_t<decltype(arg)>>::op(p, arg);
+            },
+            v);
+    }
+};
+
 } // namespace details
 
 } // namespace message