3.0.0 beta.1 API preview

[frostyplanet]

Full Changelog: v2.1.10...v3.0.0-beta.1

Because enum dispatch became a bottleneck when adding more channel flavors, I have refactored the API, which is incompatible to V2.x

https://docs.rs/crossfire/3.0.0-beta.1/crossfire/

Migration steps:
https://docs.rs/crossfire/3.0.0-beta.1/crossfire/compat/index.html

Changed

• Change interface to V3 generic flavor API

• Optimize for SPSC

Added

• Add One flavor for bounded size 1 case.

• Add Null flavor for cancellation purpose channel.

• Add Select API (currently only blocking context, only for receiver, does not support sending)

• Add Multiplex API (currently only blocking context)

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This discussion was created from the release 3.0.0 beta.1 API preview.