Returning References

In CeePlusPlus, the way one has a function return a LeftValue is by ReturningReferences. This is necessary to implement OperatorOverloading properly; OTOH this feature has some issues with it which make it ConsideredHarmful by some.

 template <class T> class myArray 
 {
     // buncha stuff not important for this example

     // need to support []
     T &operator [] (int index);

     // and for const arrays
     const T &operator [] (int index) const;

     // more
 };

In the first case, since "operator []" is declared to return a reference to T, the result can be used as a LeftValue, i.e.

 intArray a;

 a[0] = 1;
 a[1] = 2;
 cout << a[0] << "\n";
 cout << a[1] << "\n";

As expected, this program fragment prints

 1
 2

on the standard output.

ReturningReferences has quite a few issues with it, which put it firmly in the category of "use only if you know what you are doing".

• It is a common newbie error to return references to automatic variables.

 int &bad (void)
 {
      int a = 0;
      return a;
 }

 // some other function
 cout << bad();

Were we to abandon the reference type and use pointers, the equivalent C code would be

 int *bad(void)
 {
      int a = 0;
      return &a;
 }

  /* some other function */
 printf ("%d\n", *(bad()));

In both cases, a pointer to the returning function's stack frame is returned--in other words, a WildPointer.