Neverlord/libcppa — pull request #104 by mavam (2013-10-01 20:26:44+00:00)
Title: Allow for default construction of optional<T>.

In order to comply with the interface of `std::optional`, we should make it possible to default-construct optional objects. The post-condition shall be the same as in the standard: the object is an a *disengaged* state.

Achieving this involves either adding an explicit default constructor or providing a default argument for the `none_t` overload. This patch uses the latter technique.