Exception guarantees

[Morwenn]

Currently cpp-sort provides no specific guarantee about its sorting algorithms when an exception is thrown except the no-leak guarantee (all the memory allocated by the sorting algorithms is freed when an exception occurs).

While making every algorithm noexcept is impossible, it should still be possible to improve the library with regard to exception safety:

• Analyze and document the current guarantees
• Check whether simple algorithms can be conditionally noexcept (it may depend on too many things)
• When values are moved from a collection and back into it, check whether it is possible to make some algorithms put the extracted values back into the collection, albeit in an unspecified order

No matter what is or isn't done, we need to be more specific in the documentation.

[Morwenn]

Making algorithms conditionally noexcept seems difficult. When an algorithm doesn't throw std::bad_alloc, the following operations might still throw:

• The comparison function
• The projection function
• Operations on iterators
• Move & swap operations

While it might be possible to provide better guarantees when the comparison or projection functions throw, I'm not sure that it is worth it. Recovering when a move or swap throw seems impossible. I guess that I will merely document what can happen with algorithms and let it be.