defer.h

#ifndef UTIL_DEFER_H
#define UTIL_DEFER_H


#define DEFER const auto DEFER_CAT_ID(callOnScopeExit, __LINE__) = (Util::tagClassForLambda)->*[&]()
 
//==============================================================================
// Implementation details follow
 
// Helper macro to expand and concatenate macro arguments into combined identifier
#define DEFER_CAT_ID(a, b) DEFER_CAT_ID_EXPANDED_HELPER(a, b)
// helper macro to concatenate expanded macro arguments
#define DEFER_CAT_ID_EXPANDED_HELPER(a, b) a##b
 
namespace Util {
struct TagClassForLambda {
    constexpr TagClassForLambda() = default;
};


constexpr TagClassForLambda tagClassForLambda;

template <class Lambda> struct CallOnScopeExit {

    constexpr CallOnScopeExit(Lambda initialLambda)
    : lambda(initialLambda)
    , isOwner(true) {}

    CallOnScopeExit(CallOnScopeExit&& other)
    : lambda(other.lambda)
    , isOwner(true) {
        other.isOwner = false;
    }
 
    // ensure copy changes go only through move constructor
    CallOnScopeExit(const CallOnScopeExit& other) = delete;
    CallOnScopeExit& operator=(const CallOnScopeExit& other) = delete;

    ~CallOnScopeExit() {
        if(isOwner) { // condition is usually optimized away
            lambda();
        }
    }
 
private:
    const Lambda lambda; 
    bool isOwner;        
};


template <class Lambda> constexpr CallOnScopeExit<Lambda> operator->*(const TagClassForLambda&, Lambda lambda) {
    return CallOnScopeExit<Lambda>(lambda);
}
} // namespace Util
#endif // UTIL_DEFER_H