later 1.4.0

• Adds later_fd() which executes a function when a file descriptor is ready for reading or writing, at some indeterminate time in the future (subject to an optional timeout). This facilitates an event-driven approach to asynchronous or streaming downloads. (@shikokuchuo and @jcheng5, #190)

• Fixed #186: Improvements to package load time as rlang is now only loaded when used. This is a notable efficiency for packages with only a 'linking to' dependency on later. Also updates to native symbol registration from dynamic lookup. (@shikokuchuo and @wch, #187)

• Fixed #191: Errors raised in later callbacks were being re-thrown as generic C++ std::runtime_error with Rcpp >= 1.0.10 (since 2022!). (@shikokuchuo and @lionel-, #192)