Hi Mirek,

Thanks for looking into this. I really have trouble and feel insecure about returning Null references. The access to Array and Vector containers comes as references. So, when I create a function returning those references, I need to be able to return Null if the container does not have a suitable object to return for a request.

However, returning a Null reference is not trivial. And possibly also forbidden in C++. Then, I looked at using pointers instead and found that C++ references have the following limitation:

"There shall be no references to references, no arrays of references, and no pointers to references. " (ISO C++)

Finally (after quite a few hours) I came up with the following solution: Using: " return (A&)Null; " to return a Null reference. How dangerous is this? (I also added the check: " this==&(classname&)Null " to IsNullInstance() in order to cover this case.

In contrast to the previous code the following compiles with CLANG too and seems to work as expected:

#include <Core/Core.h>

using namespace Upp;

#define NULLSUPPORT(classname, variable)\
	classname(const Nuller&) { variable=Null; }\
	void SetNull() { variable=Null; }\
	bool IsNullInstance() const { return this==&(classname&)Null || IsNull(variable); }

class A{
public:
	int a;
	int b;

	NULLSUPPORT(A,a)
	
	void Clear(){ a=b=0; }
	
	A(){
		a=1;
		b=2;
	}

	void Serialize(Stream &s){
		s % a % b;
	}

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

// Testing:

Array<A> av;

A& GetA1(int x){
	if((x<0)||(x>=av.GetCount())) return (A&)Null;
	return 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++){ A &a=GetA1(i); Cout() << a << "\n"; }
	return;
}

But is this safe? If not, is there a decent way to do it?

Best regards,

Tom