Forward declares boost::hana::optional.  
More...
| Classes | |
| struct | boost::hana::optional< T > | 
| Optional value whose optional-ness is known at compile-time.  More... | |
| struct | boost::hana::optional_tag | 
| Tag representing a hana::optional.  More... | |
| Namespaces | |
| boost::hana | |
| Namespace containing everything in the library. | |
Forward declares boost::hana::optional.