Re: [Boost-users] Sequence of Types, What For?

"Arkadiy Vertleyb" writes:

"Terry G" wrote

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I've just finished reading C++ Template Metaprogramming again. I just don't get it.

Should probably not be your first book on template metaprogramming.

Really? We designed the book to serve as a complete introduction.

Really, it's just like trying to learn STL without any idea what a template is.

It's not as though the book starts out assuming you know what a metafunction is. What introductory material do you think we missed and should have covered?

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Why would someone use a type container?

For example, one could implement a generic tuple class (although I don't think boost::tuple uses this approach, but probably fusion does?). Also see below...

Of course, that begs the question of why someone would want a tuple.

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I'd really like a reference to an MPL primer or some case studies.

IMO, you should really start with template metaprogramming itself, and then move to MPL. Try Alexandrescu's "Modern C++ design" -- it also contains a lot of examples why you would want to use a typelist.

As great a book as "Modern C++ Design" is, it really surprises me to see it recommended as an introduction to template metaprogramming over "C++ Template Metaprogramming." MC++D is not about specifically TMP, and doesn't even attempt to describe what TMP is. It does contain numerous examples of basic TMP applied to traditional OO design patterns, which I think is the real point of that book, and IMO makes MC++D an ideal follow-on to C++TMP. In C++TMP we tried hard to both * define and clarify the basic concepts of TMP and * shield the reader from messy, low-level C++ details by using the MPL instead of the raw templates employed by MC++D.

Once you have a basic understanding of template metaprogramming, get back to the MPL book -- it's worth it.

Although we do spend considerable breath outlining the Boost facilities in "C++ Template Metaprogramming" (and despite the spelling of certain URLs ;-) ), we hope it won't be viewed as "the MPL book." The whole point was to treat TMP in a way that exposed its general principles and capabilities, without getting tied up in details of any particular technology, be it MPL, Loki, or raw C++ templates. -- Dave Abrahams Boost Consulting www.boost-consulting.com