A demo using const-fn as a configuration medium

The gist here:

• Embedded devices often need many tweaks to their libraries, to tune the behavior of a driver to a particular use case
  • This is often seen with things like Buffer Sizes, where sometimes 512 bytes is enough, but other times 4K is needed
• Cargo's cfg feature flags are binary, and act as a union, so it is hard to provide compile-time settings, especially non-binary ones like size parameters, via feature flags
• min_const_fn just stabilized, and will make it in time for 1.31

This demo is a PoC of using const fn to tweak compile time settings of a library, rather than relying solely on cfg features.

The parts of this demo

1. mcf-config-demo-lib - an example library, published on crates.io
2. mcf-config-demo-settings - a library crate, published on crates.io, containing default settings
3. mcf-config-demo-app - a binary crate, that consumes the library above (not published on crates.io)
4. mcf-config-demo-override - a copy of mcf-config-demo-settings, but with some configuration items changed

To see how the demo works:

$ cd mcf-config-demo-app
$ cargo run

$ cargo run
        Finished dev [unoptimized + debuginfo] target(s) in 0.00s
         Running `target/debug/mcf-config-demo-app`
    000: 0xac
    001: 0xac
    002: 0xac
    003: 0xac
    004: 0xac
    005: 0xac
    006: 0xac
    007: 0xac
    Hello, world!

# uncomment the lines from Cargo.toml in the app folder
nano Cargo.toml
# ...

cargo run
cargo run
        Finished dev [unoptimized + debuginfo] target(s) in 0.01s
         Running `target/debug/mcf-config-demo-app`
    000: 0xac
    001: 0xac
    002: 0xac
    003: 0xac
    004: 0xac
    005: 0xac
    006: 0xac
    007: 0xac
    008: 0xac
    009: 0xac
    010: 0xac
    011: 0xac
    012: 0xac
    013: 0xac
    014: 0xac
    015: 0xac
    y halo thar!

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)

• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

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.