2 releases
0.1.1 | Apr 13, 2022 |
---|---|
0.1.0 | Feb 8, 2021 |
#168 in No standard library
115KB
84 lines
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 } => {
// ...
},
}