Hello, Library Crate!

Prerequisite: As always, we assume that we are working inside a terminal session running in our usual Docker container (as previously explained in Development Environment Setup).

Source code at `rust_playground/rs-ws/my_lib

A library crate provides reusable functionality that can be shared across multiple projects or binaries.

To create a new library crate, we can run:

cd rs-ws
cargo new my_lib --lib

resulting in the creation of a crate having only one source file rs-ws/my_lib/src/lib.rs:

#![allow(unused)]
fn main() {
pub fn add(left: u64, right: u64) -> u64 {
    left + right
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn it_works() {
        let result = add(2, 2);
        assert_eq!(result, 4);
    }
}
}

As we can see, by default the library crate has an add function, as well as an it_works test function, which is a unit test for add.

As for a binary crate, we can format:

cargo fmt --verbose --package my_lib

and we can run Clippy lints:

cargo clippy --verbose --package my_lib --release

and we can check the crate:

cargo check --package my_lib --release

or we can build it:

cargo build --package my_lib --release

In addition, we can run the tests:

cargo test --package my_lib --release

Get a line coverage report:

cargo llvm-cov --package my_lib --release

And, last but not least, we can automatically generate the documentation:

cargo doc --package my_lib --no-deps --release

that will end up in rust_playground/target/doc/my_lib, and we can serve the docs by:

python3 -m http.server 8080 -d /root/rust_playground/target/doc

and read them by opening a browser and navigating to http://localhost:8080/my_lib/index.html.

Create a binary crate depending on this library

Source code at `rust_playground/rs-ws/my_app

Now, we can create a new binary crate that depends on the library crate we just created. It is really easy to do so in a workspace.

Let us start by creating my_app:

cd rs-ws
cargo new my_app --bin

Then, navigate to its Cargo.toml file (at [rust_playground/rs-ws/my_app/Cargo.toml](https://github.com/ilarioazzollini/rust_playground/tree/main/rs-ws/my_app/Cargo.toml)), and under the dependenciessection, add a dependency onmy_lib` as follows:

[dependencies]
my_lib = { path = "../my_lib" }

Now, we can modify the `rust_playground/rs-ws/my_app/src/main.rs file as follows:

fn main() {
    let number_1: u64 = 2;
    let number_2: u64 = 1;

    let result: u64 = my_lib::add(number_1, number_2);
    println!(
        "Added numbers '{}' and '{}', and got the result: '{}'",
        number_1, number_2, result
    );
}

and we should be able to compile it and run it:

cargo run --package my_app --release

Useful References

There are many important aspects to consider while developing a library crate. Some useful references are:

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Rust Playground

Hello, Library Crate!

Create a binary crate depending on this library

Useful References