Add idioms notes

Author: bc913

README.md

@@ -31,6 +31,8 @@ This repo reflects some of the best practices for C++ based on my knowledge and
 
 [Misc](notes/Misc.md)
 
+[Idioms](notes/Idioms.md)
+
 ## Build
 ### Linux
 ```bash

notes/Idioms.md

@@ -0,0 +1,135 @@
+# Idioms
+
+## (A possible) Generic implementation for flags
+
+First make sure that the `underlying_type` of the enum is unsigned integer.
+
+```cpp
+enum class MyFlags : unsigned int {
+    None = 0,
+    Flag1 = 1 << 0,  // 0001
+    Flag2 = 1 << 1,  // 0010
+    Flag3 = 1 << 2,  // 0100
+    Flag4 = 1 << 3   // 1000
+};
+```
+
+Using `<type_traits>` might provide a solution to achieve a generic implementation for flag enums.
+
+- Solution 1:
+
+```cpp
+#include <type_traits>
+
+template<typename T, typename ULT = unsigned int>
+struct is_flag_type : std::integral_constant<bool, (std::is_enum_v<T>) && (std::is_same_v<std::underlying_type_t<T>, ULT>)> {};
+
+template<typename T, typename ULT = unsigned int, std::enable_if_t<is_flag_type<T,ULT>::value, bool> = true>
+inline T operator|(T lhs, T rhs) {
+    return static_cast<T>(static_cast<ULT>(lhs) | static_cast<ULT>(rhs));
+}
+
+template<typename T, typename ULT = unsigned int, std::enable_if_t<is_flag_type<T,ULT>::value, bool> = true>
+inline T operator&(T lhs, T rhs) {
+    return static_cast<T>(static_cast<ULT>(lhs) & static_cast<ULT>(rhs));
+}
+
+template<typename T, typename ULT = unsigned int, std::enable_if_t<is_flag_type<T,ULT>::value, bool> = true>
+inline T operator~(T rhs) {
+    return static_cast<T>(~static_cast<ULT>(rhs));
+}
+
+template<typename T, typename ULT = unsigned int, std::enable_if_t<is_flag_type<T,ULT>::value, bool> = true>
+inline T& operator|=(T& lhs, T rhs) {
+    lhs = lhs | rhs;
+    return lhs;
+}
+
+template<typename T, typename ULT = unsigned int, std::enable_if_t<is_flag_type<T,ULT>::value, bool> = true>
+inline T& operator&=(T& lhs, T rhs) {
+    lhs = lhs & rhs;
+    return lhs;
+}
+
+//=====================
+template<typename T, typename ULT = unsigned int, std::enable_if_t<is_flag_type<T,ULT>::value, bool> = true>
+inline T& SetFlag(T& lhs, T rhs)
+{
+    return lhs |= rhs;
+}
+
+template<typename T, typename ULT = unsigned int, std::enable_if_t<is_flag_type<T,ULT>::value, bool> = true>
+inline T& UnSetFlag(T& lhs, T rhs)
+{
+    return lhs &= ~rhs;
+}
+
+template<typename T, typename ULT = unsigned int, std::enable_if_t<is_flag_type<T,ULT>::value, bool> = true>
+inline bool IsFlagSet(T flag, T check)
+{
+    return (flag & check) == check;
+}
+
+```
+
+- Solution 2 (A bit cleaner):
+
+```cpp
+template<typename T>
+struct is_flag_type2 : std::integral_constant<bool, (std::is_enum_v<T>) && (std::is_unsigned_v<std::underlying_type_t<T>>)> {};
+
+
+template<typename T, std::enable_if_t<is_flag_type2<T>::value, bool> = true>
+inline T operator|(T lhs, T rhs) {
+    return static_cast<T>(static_cast<std::underlying_type_t<T>>(lhs) | static_cast<std::underlying_type_t<T>>(rhs));
+}
+
+template<typename T, std::enable_if_t<is_flag_type2<T>::value, bool> = true>
+inline T operator&(T lhs, T rhs) {
+    return static_cast<T>(static_cast<std::underlying_type_t<T>>(lhs) & static_cast<std::underlying_type_t<T>>(rhs));
+}
+
+template<typename T, std::enable_if_t<is_flag_type2<T>::value, bool> = true>
+inline T operator~(T rhs) {
+    return static_cast<T>(~static_cast<std::underlying_type_t<T>>(rhs));
+}
+
+template<typename T, std::enable_if_t<is_flag_type2<T>::value, bool> = true>
+inline T& operator|=(T& lhs, T rhs) {
+    lhs = lhs | rhs;
+    return lhs;
+}
+
+template<typename T, std::enable_if_t<is_flag_type2<T>::value, bool> = true>
+inline T& operator&=(T& lhs, T rhs) {
+    lhs = lhs & rhs;
+    return lhs;
+}
+//=====================
+template<typename T, std::enable_if_t<is_flag_type2<T>::value, bool> = true>
+inline T& SetFlag(T& lhs, T rhs)
+{
+    return lhs |= rhs;
+}
+
+template<typename T, std::enable_if_t<is_flag_type2<T>::value, bool> = true>
+inline T& UnSetFlag(T& lhs, T rhs)
+{
+    return lhs &= ~rhs;
+}
+
+template<typename T, std::enable_if_t<is_flag_type2<T>::value, bool> = true>
+inline bool IsFlagSet(T flag, T check)
+{
+    return (flag & check) == check;
+}
+```
+
+- Usage:
+
+```cpp
+MyFlags flags = MyFlags::None;
+SetFlag<MyFlags>(flags, MyFlags::Flag1);
+UnSetFlag<MyFlags>(flags, MyFlags::Flag1);
+auto res = IsFlagSet<MyFlags>(flags, MyFlags::Flag2);
+```