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Re: About Nuller and Null [message #55095 is a reply to message #55094]

Sun, 11 October 2020 00:02

Tom1
Messages: 1305
Registered: March 2007

Ultimate Contributor

Hi,

How about this? I did not benchmark the performance, but at least this is not relying on testing for a Null reference. As you can see, the 'Optional' is named in the foot steps of std::optional which is available in C++17 for the same purpose. (However, std::optional does not seem to support passing reference variables.)

#include <Core/Core.h>

using namespace Upp;

template <typename T>
struct Optional : public Tuple2<bool, T>{
	typedef Tuple2<bool, T> Base;
	Optional(T data) : Base(true, data) { }
	Optional() : Base(false, (T)Null) { }
	inline bool	IsOK(){ return (bool)Base::a; }
	inline T	Get(){ return (T)Base::b; }
};

class A{
public:
	int a;
	int b;
	
	A(){
		a=1;
		b=2;
	}

	String ToString() const { return String("A[") << a << ", " << b << "]"; }
};

// Testing:

Array<A> av;

Optional<A&> GetA2(int x){
	if((x<0)||(x>=av.GetCount())) return Optional<A&>();
	return Optional<A&>(av[x]);
}

CONSOLE_APP_MAIN{
	av.Add().a=1;
	av.Add().a=2;
	av.Add().a=3;
	av.Add().a=4;

	for(int i=-1;i<6;i++){ 
		Optional<A&> result=GetA2(i); 
		Cout() << (result.IsOK() ? AsString(result.Get()) : "Null") << "\n"; 
	}
}

Best regards,

Tom

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