use C++11 constexpr to replace static typeCode

clang-cl has a problem with static memeber variable
llvm/llvm-project#54814.
But it has no problem with constexpr member variable.

Author: xiaoqiangwang

src/factory/PVDataCreateFactory.cpp

@@ -30,7 +30,7 @@ using std::min;
 
 namespace epics { namespace pvData {
 
-
+#if __cplusplus < 201103L
 template<> const ScalarType PVBoolean::typeCode = pvBoolean;
 template<> const ScalarType PVByte::typeCode = pvByte;
 template<> const ScalarType PVShort::typeCode = pvShort;
@@ -56,7 +56,7 @@ template<> const ScalarType PVULongArray::typeCode = pvULong;
 template<> const ScalarType PVFloatArray::typeCode = pvFloat;
 template<> const ScalarType PVDoubleArray::typeCode = pvDouble;
 template<> const ScalarType PVStringArray::typeCode = pvString;
-
+#endif
 
 template<typename T>
 PVScalarValue<T>::~PVScalarValue() {}

src/pv/pvData.h

@@ -16,6 +16,9 @@
 #include <iterator>
 #include <iostream>
 #include <iomanip>
+#if __cplusplus >= 201103L
+#include <type_traits>
+#endif
 
 #include <epicsAssert.h>
 
@@ -124,6 +127,36 @@ typedef std::tr1::shared_ptr<PVUnionArrayPtrArray> PVUnionArrayPtrArrayPtr;
 class PVDataCreate;
 typedef std::tr1::shared_ptr<PVDataCreate> PVDataCreatePtr;
 
+#if __cplusplus >= 201103L
+template <typename T>
+constexpr ScalarType typeToCode() {
+    if (std::is_same<T, boolean>::value)
+        return pvBoolean;
+    else if (std::is_same<T, int8>::value)
+        return pvByte;
+    else if (std::is_same<T, uint8>::value)
+        return pvUByte;
+    else if (std::is_same<T, int16>::value)
+        return pvShort;
+    else if (std::is_same<T, uint16>::value)
+        return pvUShort;
+    else if (std::is_same<T, int32>::value)
+        return pvInt;
+    else if (std::is_same<T, uint32>::value)
+        return pvUInt;
+    else if (std::is_same<T, int64>::value)
+        return pvLong;
+    else if (std::is_same<T, uint64>::value)
+        return pvULong;
+    else if (std::is_same<T, float>::value)
+        return pvFloat;
+    else if (std::is_same<T, double>::value)
+        return pvDouble;
+    else if (std::is_same<T, std::string>::value)
+        return pvString;
+}
+#endif
+
 /**
  * @brief This class is implemented by code that calls setPostHander
  *
@@ -383,7 +416,11 @@ class epicsShareClass PVScalarValue : public PVScalar {
     typedef T* pointer;
     typedef const T* const_pointer;
 
+    #if __cplusplus < 201103L
     static const ScalarType typeCode;
+    #else
+    constexpr static const ScalarType typeCode = typeToCode<T>();
+    #endif
 
     /**
      * Destructor
@@ -1184,8 +1221,11 @@ class epicsShareClass PVValueArray : public detail::PVVectorStorage<T,PVScalarAr
     typedef ::epics::pvData::shared_vector<T> svector;
     typedef ::epics::pvData::shared_vector<const T> const_svector;
 
-
+    #if __cplusplus < 201103L
     static const ScalarType typeCode;
+    #else
+    constexpr static const ScalarType typeCode = typeToCode<T>();
+    #endif
 
     /**
      * Destructor