Returning a “NULL reference” in C++?

Question

In dynamically typed languages like JavaScript or PHP, I often do functions such as:

function getSomething(name) {
    if (content_[name]) return content_[na         


        

Answer 1

Why "besides using pointers"? Using pointers is the way you do it in C++. Unless you define some "optional" type which has something like the isNull() function you mentioned. (or use an existing one, like boost::optional)

References are designed, and guaranteed, to never be null. Asking "so how do I make them null" is nonsensical. You use pointers when you need a "nullable reference".

Answer 2

Here are a couple of ideas:

Alternative 1:

class Nullable
{
private:
    bool m_bIsNull;

protected:
    Nullable(bool bIsNull) : m_bIsNull(bIsNull) {}
    void setNull(bool bIsNull) { m_bIsNull = bIsNull; }

public:
    bool isNull();
};

class SomeResource : public Nullable
{
public:
    SomeResource() : Nullable(true) {}
    SomeResource(...) : Nullable(false) { ... }

    ...
};

Alternative 2:

template<class T>
struct Nullable<T>
{
    Nullable(const T& value_) : value(value_), isNull(false) {}
    Nullable() : isNull(true) {}

    T value;
    bool isNull;
};