AMDG James Porter wrote:
There are a number of issues that make this a fairly complicated problem, even with the improved generic programming facilities in C++0x. Chief among these is copying. With the naive implementation of the memoizer, I found that calculating the result of an unmemoized value created 3 copies (one for creating a tuple to search a map for, and two to insert the tuple into the map), and returning a memoized value created 1 copy (to create a tuple to search the map).
To make a long story short, I set about trying to reduce the number of copies to the expected amount: 1 copy for unmemoized values and 0 for memoized values. I'm happy to say that this was a success! The trick was creating a tuple that holds references to each argument and can be upgraded to hold the arguments by value. In this way, we can compare by reference and store by value. This is simple on the surface, but requires some care when dealing with rvalue references.
You might want to look at Boost.Intrusive, which allows you to avoid the extra copies without adding indirection. http://www.boost.org/doc/html/intrusive/advanced_lookups_insertions.html In Christ, Steven Watanabe