Boost
C++ Libraries
...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
This is an older version of Boost and was released in 2017. The current version is 1.90.0.
The return type of an initiating function is typename async_result<decay_t<CompletionToken>,
Signature>::return_type.
For the sake of exposition, this library sometimes annotates functions
with a return type DEDUCED. For
every function declaration that returns DEDUCED,
the meaning is equivalent to specifying the return type as typename
async_result<decay_t<CompletionToken>, Signature>::return_type.