4 releases
0.1.3 | Apr 20, 2023 |
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0.1.2 | Jun 30, 2022 |
0.1.1 | Jun 30, 2022 |
0.1.0 | Jun 30, 2022 |
#2865 in Rust patterns
7KB
84 lines
Maybe static
Initialize in a lazy way a static variable with parameters.
Example of a simple usage:
use maybe_static::maybe_static;
pub fn get_lazy(opt: Option<(&str, &str)>) -> Result<&'static String, &'static str> {
maybe_static!(opt, String, |(a, b)| format!("{a}:{b}"))
}
fn main() {
println!("{}", get_lazy(Some(("hello", "world"))).unwrap());
println!("{}", get_lazy(None).unwrap());
}
The macro will create a local static variable that is initialized once, ONLY ONCE. It's also totally thread safe.
fn main() {
println!("{}", get_lazy(Some(("hello", "world"))).unwrap());
// print hello:world (initialize)
println!("{}", get_lazy(None).unwrap());
// print hello:world
println!("{}", get_lazy(Some(("foo", "bar"))).unwrap());
// still print hello:world
}
Require a Some
for the first initialization.
fn main() {
println!("{}", get_lazy(None).unwrap()); // Error!
}
Create a new unique value by scope.
fn main() {
let a = maybe_static!(Some(("hello", "world")), String, |(a, b)| format!(
"{a}:{b}"
))
.unwrap();
let b = maybe_static!(Some(("foo", "bar")), String, |(a, b)| format!(
"{a}:{b}"
))
.unwrap();
println!("{a}\n{b}")
// hello:world
// foo:bar
for i in 0..3 {
print!("{}", maybe_static!(Some(i), usize, |i| i).unwrap());
}
// 000
}
Initially developed around the article in the maybeuninit blog