defer macro

defer.h

//from https://pastebin.com/3YvWQa5c

#define CONCAT_INTERNAL(x,y) x##y
#define CONCAT(x,y) CONCAT_INTERNAL(x,y)
 
template<typename T>
struct ExitScope {
    T lambda;
    ExitScope(T lambda):lambda(lambda){}
    ~ExitScope(){lambda();}
    ExitScope(const ExitScope&);
  private:
    ExitScope& operator =(const ExitScope&);
};
 
class ExitScopeHelp {
  public:
    template<typename T>
        ExitScope<T> operator+(T t){ return t;}
};
 
#define defer const auto& CONCAT(defer__, __LINE__) = ExitScopeHelp() + [&]()
 
//USE: 
// auto tools_filename = malloc(42);
// defer { free(tools_filename); };