5 releases
0.1.4 | Nov 2, 2023 |
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0.1.3 | Nov 2, 2023 |
0.1.2 | Nov 2, 2023 |
0.1.1 | Oct 30, 2023 |
0.1.0 | Oct 30, 2023 |
#170 in #lazy-evaluation
Used in lazy-attribute
10KB
86 lines
lazy-attributes
provides attribute macros for simplifying working with lazily evaluated functions.
Functions decorated with #[lazy_ref]
will only be executed the first time they are called.
On subsequent calls, the cached return value is returned.
Usage
With lazy_attribute::lazy_ref
, you can annotate a function that you want to lazily evaluate:
use lazy_attribute::lazy_ref;
#[lazy_ref]
fn get_string() -> String {
println!("Called once!");
String::from("Hello, world!")
}
fn main() {
println!("{}", get_string()); // Outputs: Called once! Hello, world!
println!("{}", get_string()); // Outputs: Hello, world!
}
The first time the function is called, it will be evaluated and its result will be cached. Subsequent calls will return the cached result.
lazy_ref
macro roughly desugars the get_string
function to:
static __lazy_static_get_string: OnceCell<String> = OnceCell::new();
fn get_string() -> &'static String {
__lazy_static_get_string.get_or_init(|| {
println!("Called once!");
String::from("Hello, world!")
})
}
With async
feature enabled, lazy_ref
can also be used with async functions:
use lazy_attribute::lazy_ref;
#[lazy_ref]
async fn get_string() -> String {
println!("Called once!");
String::from("Hello, world!")
}
#[tokio::main]
async fn main() {
println!("{}", get_string().await); // Outputs: Called once! Hello, world!
println!("{}", get_string().await); // Outputs: Hello, world!
}
Caveats
lazy_*
macros do not support functions with arguments. You will get an error telling you arguments are not supported.
Crate Features
async
- Enables support for lazily evaluating async functions.
Dependencies
~3MB
~56K SLoC