Question

From the discussion that has happened in my recent question (Why is a c++ reference considered safer than a pointer?), it raises another question in my mind: What exactly was the rationale behind introducing references in c++?

Answer 1

Section 3.7 of Stroustrup’s Design and Evolution of C++ describes the introduction of references into the language. If you’re interested in the rationale behind any feature of C++, I highly recommend this book.

References were introduced primarily to support operator overloading. Doug McIlroy recalls that once I was explaining some problems with a precursor to the current operator overloading scheme to him. He used the word reference with the startling effect that I muttered "Thank you," and left his office to reappear the next day with the current scheme essentially complete. Doug had reminded me of Algol68.

C passes every function argument by value, and where passing an object by value would be inefficient or inappropriate the user can pass a pointer. This strategy doesn’t work where operator overloading is used. In that case, notational convenience is essential because users cannot be expected to insert address-of operators if the objects are large. For example:

a = b - c;

is acceptable (that is, conventional) notation, but

a = &b - &c;

is not. Anyway, &b - &c already has a meaning in C, and I didn’t want to change that.

It is not possible to change what a reference refers to after initialization. That is, once a C++ reference is initialized, it cannot be re-bound. I had in the past been bitten by Algol68 references where r1 = r2 can either assign through r1 to the object referred to or assign a new reference value to r1 (re-binding r1) depending on the type of r2. I wanted to avoid such problems in C++.