[ALACPP] Latest CUJ doing sorting with typelists.

[Christopher Smith <x@xxxxxxxx>]

So, I didn't get much sleep last night, and for the first part of it I
decided to read my latest CUJ. It has a number of interesting articles
in it which various members of this group would like (like an article on
Boost.Python, and another on custom memory allocators). The one that
really caught my eye though was an article about using typelists to do
sorting.

C++ sorting is typically done with functors, so what this article talks
about is using a typelist to chain together a variety of sort functors.
So, you could do something like TYPELIST_2(less_last, less_first) to
instantiate a sorter which sorts on last name, then first name,
essentially using the Chain-of-Command pattern.

This struck me as a specific instantiation of what I was talking about
yesterday: namely static functors, using template parameters instead of
instance variables. This allows you to define a templated "map" class
that allows you to chain together a series of functors using a typelist.
The nice thing is that it's all evaluated at compile time, so you get
the benefits of polymorphism without the overhead of a virtual function
table (indeed, in a lot of cases function calls will get inlined).

--Chris
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