refactor: use "if constexpr" in std::vector's Serialize()

This gets rid of unnecessarily creating a temporary object T() to call
the right function.

Author: martinus

src/serialize.h

@@ -649,9 +649,6 @@ template<typename Stream, unsigned int N, typename T> inline void Unserialize(St
  * vector
  * vectors of unsigned char are a special case and are intended to be serialized as a single opaque blob.
  */
-template<typename Stream, typename T, typename A> void Serialize_impl(Stream& os, const std::vector<T, A>& v, const unsigned char&);
-template<typename Stream, typename T, typename A> void Serialize_impl(Stream& os, const std::vector<T, A>& v, const bool&);
-template<typename Stream, typename T, typename A, typename V> void Serialize_impl(Stream& os, const std::vector<T, A>& v, const V&);
 template<typename Stream, typename T, typename A> inline void Serialize(Stream& os, const std::vector<T, A>& v);
 template<typename Stream, typename T, typename A> void Unserialize_impl(Stream& is, std::vector<T, A>& v, const unsigned char&);
 template<typename Stream, typename T, typename A, typename V> void Unserialize_impl(Stream& is, std::vector<T, A>& v, const V&);
@@ -783,38 +780,26 @@ void Unserialize(Stream& is, prevector<N, T>& v)
 /**
  * vector
  */
-template<typename Stream, typename T, typename A>
-void Serialize_impl(Stream& os, const std::vector<T, A>& v, const unsigned char&)
-{
-    WriteCompactSize(os, v.size());
-    if (!v.empty())
-        os.write(MakeByteSpan(v));
-}
-
-template<typename Stream, typename T, typename A>
-void Serialize_impl(Stream& os, const std::vector<T, A>& v, const bool&)
+template <typename Stream, typename T, typename A>
+void Serialize(Stream& os, const std::vector<T, A>& v)
 {
-    // A special case for std::vector<bool>, as dereferencing
-    // std::vector<bool>::const_iterator does not result in a const bool&
-    // due to std::vector's special casing for bool arguments.
-    WriteCompactSize(os, v.size());
-    for (bool elem : v) {
-        ::Serialize(os, elem);
+    if constexpr (std::is_same_v<T, unsigned char>) {
+        WriteCompactSize(os, v.size());
+        if (!v.empty())
+            os.write(MakeByteSpan(v));
+    } else if constexpr (std::is_same_v<T, bool>) {
+        // A special case for std::vector<bool>, as dereferencing
+        // std::vector<bool>::const_iterator does not result in a const bool&
+        // due to std::vector's special casing for bool arguments.
+        WriteCompactSize(os, v.size());
+        for (bool elem : v) {
+            ::Serialize(os, elem);
+        }
+    } else {
+        Serialize(os, Using<VectorFormatter<DefaultFormatter>>(v));
     }
 }
 
-template<typename Stream, typename T, typename A, typename V>
-void Serialize_impl(Stream& os, const std::vector<T, A>& v, const V&)
-{
-    Serialize(os, Using<VectorFormatter<DefaultFormatter>>(v));
-}
-
-template<typename Stream, typename T, typename A>
-inline void Serialize(Stream& os, const std::vector<T, A>& v)
-{
-    Serialize_impl(os, v, T());
-}
-
 
 template<typename Stream, typename T, typename A>
 void Unserialize_impl(Stream& is, std::vector<T, A>& v, const unsigned char&)