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### Acknowledgements

##### Pre-formal review

- Peter Dimov suggested the name 'optional', and was the first to point out the need for aligned storage.
- Douglas Gregor developed 'type_with_alignment', and later Eric Friedman coded 'aligned_storage', which are the core of the optional class implementation.
- Andrei Alexandrescu and Brian Parker also worked with aligned storage techniques and their work influenced the current implementation.
- Gennadiy Rozental made extensive and important comments which shaped the design.
- Vesa Karvonen and Douglas Gregor made quite useful comparisons between optional, variant and any; and made other relevant comments.
- Douglas Gregor and Peter Dimov commented on comparisons and evaluation in boolean contexts.
- Eric Friedman helped understand the issues involved with aligned storage, move/copy operations and exception safety.
- Many others have participated with useful comments: Aleksey Gurotov, Kevlin Henney, David Abrahams, and others I can't recall.

##### Post-formal review

- William Kempf carefully considered the originally proposed interface and suggested the new interface which is currently used. He also started and fueled the discussion about the analogy optional<>/smart pointer and about relational operators.
- Peter Dimov, Joel de Guzman, David Abrahams, Tanton Gibbs and Ian Hanson focused on the relational semantics of optional (originally undefined); concluding with the fact that the pointer-like interface doesn't make it a pointer so it shall have deep relational operators.
- Augustus Saunders also explored the different relational semantics between optional<> and a pointer and developed the OptionalPointee concept as an aid against potential conflicts on generic code.
- Joel de Guzman noticed that optional<> can be seen as an API on top of variant<T,nil_t>.
- Dave Gomboc explained the meaning and usage of the Haskell analog to optional<>: the Maybe type constructor (analogy originally pointed out by David Sankel).
- Other comments were posted by Vincent Finn, Anthony Williams, Ed Brey, Rob Stewart, and others.
- Joel de Guzman made the case for the support of references and helped with the proper semantics.
- Mat Marcus shown the virtues of a value-oriented interface, influencing the current design, and contributed the idea of "none".
- Vladimir Batov's design of Boost.Convert library motivated the development of value accessors for `optional`: functions `value`, `value_or`, `value_or_eval`.