futures-compat-experiment

This library is an experiment to make core::{future, task} available in a version that is not yet stable in the standard library.

The purpose of this library is to allow experiment with how the Stream trait re-export proposed in rust-lang/futures-rs#2207 works.

In that proposal, once the std Stream trait is stable, futures_core::Stream is replaced with re-export from the standard library. In the version that has stable std Stream, std Stream and futures_core::Stream is the same trait.

This should ideally be implemented by using cfg-accessible, but it's not yet stable, so use a build script.

Known limitations/issues

Known limitations/issues when applying this way to Stream trait are:

• This way will not work if the std Stream trait changes after the Stream trait is published as part of futures_core v1. See also this comment in rust-lang/futures-rs#2207.

• If use this way, the build script that detect std Stream must be enabled from the first release of that major version (even if the Straem trait is not yet implemented in std). Otherwise, the compile may fail if it relies on an older version of the library.

• If you rely on both the Stream trait provided by the futures_core and the unstable std Stream, the compile will successful while std Stream trait is unstable, the compile will fail when the Stream trait stabilizes.

  #![feature(stream_trait)]
  impl core::stream::Stream for Type { ... }
  impl futures_core::Stream for Type { ... }

  Note: This issue does not occur unless you rely on the unstable feature of the standard library. (They are the same trait from the beginning)

• If you are using a build system that does not support build scripts, if you don't update the compiler and dependencies at the same time, the compile will fail when the Stream trait stabilizes.

  Note: If build-script works, it should be able to detect it properly. So similar issues should not occur.

• If you are using a build system that does not support build scripts, a guaranteed MSRV is basically the latest stable compiler.

  (Of course, if build-script works, it can basically compile with older compilers.)

Known issues when using this crate with 1.33 (MSRV) - 1.35 compilers are:

• If you are using a build system that does not support build scripts, this crate will not be available in Rust 1.33 - 1.35.

• Features that depend on features that are not stable in those versions are not available:

  • RawWakerVTable::new is not const as function pointers in const fn are unstable in those version.
  • Try trait is not stable yet. so the following impls does is not provided.
    • impl<T, E> Try for Poll<Result<T, E>>
    • impl<T, E> Try for Poll<Option<Result<T, E>>>

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.