Disable templetized operators by default

To avoid nasty bugs due to silently overriding of
common operator we enable the templates on a type
by type base using partial template specialization.

No functional change, zero overhead at runtime.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/types.h

@@ -112,43 +112,61 @@ inline void __cpuid(int CPUInfo[4], int)
 
 // Templetized operators used by enum types like Depth, Piece, Square and so on.
 // We don't want to write the same inline for each different enum. Note that we
-// pass by value (to silence scaring warnings on volatiles), so you really should
-// use only enum types with these functions to avoid hidden copies.
+// pass by value to silence scaring warnings when using volatiles.
+// Because these templates override common operators and are included in all the
+// files, there is a possibility that the compiler silently performs some unwanted
+// overrides. To avoid possible very nasty bugs the templates are disabled by default
+// and must be enabled for each type on a case by case base. The enabling trick
+// uses template specialization, namely we just declare following struct.
+template<typename T> struct TempletizedOperator;
+
+// Then to enable the enum type we use following macro that defines a specialization
+// of TempletizedOperator for the given enum T. Here is defined typedef Not_Enabled.
+// Name of typedef is chosen to produce somewhat informative compile error messages.
+#define ENABLE_OPERATORS_ON(T)  \
+        template<> struct TempletizedOperator<T> { typedef T Not_Enabled; }
+
+// Finally we use macro OK(T) to check if type T is enabled. The macro simply
+// tries to use Not_Enabled, if was not previously defined a compile error occurs.
+// The check is done fully at compile time and there is zero overhead at runtime.
+#define OK(T) typedef typename TempletizedOperator<T>::Not_Enabled Type
 
 template<typename T>
-inline T operator+ (const T d1, const T d2) { return T(int(d1) + int(d2)); }
+inline T operator+ (const T d1, const T d2) { OK(T); return T(int(d1) + int(d2)); }
 
 template<typename T>
-inline T operator- (const T d1, const T d2) { return T(int(d1) - int(d2)); }
+inline T operator- (const T d1, const T d2) { OK(T); return T(int(d1) - int(d2)); }
 
 template<typename T>
-inline T operator* (int i, const T d) { return T(i * int(d)); }
+inline T operator* (int i, const T d) { OK(T); return T(i * int(d)); }
 
 template<typename T>
-inline T operator* (const T d, int i) { return T(int(d) * i); }
+inline T operator* (const T d, int i) { OK(T); return T(int(d) * i); }
 
 template<typename T>
-inline T operator/ (const T d, int i) { return T(int(d) / i); }
+inline T operator/ (const T d, int i) { OK(T); return T(int(d) / i); }
 
 template<typename T>
-inline T operator- (const T d) { return T(-int(d)); }
+inline T operator- (const T d) { OK(T); return T(-int(d)); }
 
 template<typename T>
-inline void operator++ (T& d, int) { d = T(int(d) + 1); }
+inline void operator++ (T& d, int) { OK(T); d = T(int(d) + 1); }
 
 template<typename T>
-inline void operator-- (T& d, int) { d = T(int(d) - 1); }
+inline void operator-- (T& d, int) { OK(T); d = T(int(d) - 1); }
 
 template<typename T>
-inline void operator+= (T& d1, const T d2) { d1 = d1 + d2; }
+inline void operator+= (T& d1, const T d2) { OK(T); d1 = d1 + d2; }
 
 template<typename T>
-inline void operator-= (T& d1, const T d2) { d1 = d1 - d2; }
+inline void operator-= (T& d1, const T d2) { OK(T); d1 = d1 - d2; }
 
 template<typename T>
-inline void operator*= (T& d, int i) { d = T(int(d) * i); }
+inline void operator*= (T& d, int i) { OK(T); d = T(int(d) * i); }
 
 template<typename T>
-inline void operator/= (T& d, int i) { d = T(int(d) / i); }
+inline void operator/= (T& d, int i) { OK(T); d = T(int(d) / i); }
+
+#undef OK
 
 #endif // !defined(TYPES_H_INCLUDED)