16.5 Afternotes

Ru-Brd

Named template arguments are used to simplify certain class templates in the Boost library. Boost uses metaprogramming to create a type with properties similar to our PolicySelector (but without using virtual inheritance). The simpler alternative presented here was developed by one of us (Vandevoorde).

CRTPs have been in use since at least 1991. However, James Coplien was first to describe them formally as a class of so-called patterns (see [CoplienCRTP]). Since then, many applications of CRTP have been published. The phrase parameterized inheritance is sometimes wrongly equated with CRTP. As we have shown, CRTP does not require the derivation to be parameterized at all, and many forms of parameterized inheritance do not conform to CRTP. CRTP is also sometimes confused with the Barton-Nackman trick (see Section 11.7 on page 174) because Barton and Nackman frequently used CRTP in combination with friend name injection (and the latter is an important component of the Barton-Nackman trick). Our ObjectCounter example is almost identical to a technique developed by Scott Meyers in [MeyersCounting].

Bill Gibbons was the main sponsor behind the introduction of EBCO into the C++ programming language. Nathan Myers made it popular and proposed a template similar to our BaseMemberPair to take better advantage of it. The Boost library contains a considerably more sophisticated template, called compressed_pair , that resolves some of the problems we reported for the MyClass template in this chapter. boost::compressed_pair can also be used instead of our BaseMemberPair .

Ru-Brd