Can you share any real-world examples of Boost::MPL usage (except lambdas), just to let me better understand its purposes and field of practical usage? The MPL documentation tutorial has a dimensional analysis example, but maybe because it's such an academic example it hasn't given me a feeling of Boost::MPL and when it can be effectively used.
I've used Boost.Mpl to generate variant-like classes.
For example, given a MPL type list such as this:
typedef boost::mpl::set<Foo, Bar, Baz> type_set;
I then use boost::mpl::fold to build a chain of classes derived from each others which each adds an std::unordered_set of one of the types in the type set. The end result is a class which contains an unordered_set<Foo>, an unordered_set<Bar> and an unordered_set<Baz>.
And because the class is specified in terms of a boost::mpl::set, I can iterate over these types to automatically generate other functions as well, such as an operator== which compares all of the unordered_sets.