Adding `kiam` library as a dependency

Run this command in a terminal, in your project's directory:

cargo add kiam

To add it manually, edit your project's Cargo.toml file and add to the [dependencies] section:

kiam = "0.1.1"

The kiam library will be automatically available globally. Read the kiam library documentation.

Back to the crate overview.

Readme

kiam

("kiam" is "when" in Esperanto)

This crate introduces when! macro which provides better syntax for if/else if/else chains. The syntax is similar to match.

(idea is borrowed from kotlin)

[dependencies] 
kiam = "0.1"

Usage

Usage is similar to the usage of match, but instead of patterns, branches are guarded by boolean expression:

kiam::when! {
    false => (),
    true => (),
    // ...
}

_ can be used as a default branch (it's also required to use when! in expression possition):

let x = kiam::when! {
    false => 0,
    _ => 1,
};

assert_eq!(x, 1);

You can also use let <pat> = to match a pattern, but in difference with match you'll have to provide an expression for every pattern:

let a = None;
let b = Some(17);
let fallible = || Err(());

let x = kiam::when! {
    let Some(x) = a => x,
    let Ok(x) = fallible() => x,
    let Some(x) = b => (x as u32) + 1,
    _ => 1,
};

assert_eq!(x, 18);

Last notes:

You can also compare structure litetals without brackets (you can't do this with if/else if/else chain)
You can mixup boolean-braches with pattern matching
Only one branch is executed (not to be confused with switch in C-like languages)

let mut x = 0;

kiam::when! {
    let Ok(_) = Err::<(), _>(()) => x = 1,
    true => x = 2,
    true => x = 3,
    let Some(n) = Some(42) => x = n,
};

assert_eq!(x, 2);

#[derive(PartialEq)]
struct Struct { a: i32 }

// This does not compile because of the ambiguity
if Struct { a: 0 } == Struct { a: 0 } {
    // ...
}

#[derive(PartialEq)]
struct Struct { a: i32 }

kiam::when! {
    // This, on the other hand, compiles fine
    Struct { a: 0 } == Struct { a: 0 } => {
        // ...
    },
}

Adding kiam library as a dependency

Adding `kiam` library as a dependency