[−][src]Crate sloth
This crate provides a generic pointer-like Lazy<T, Eval>
struct for lazily initialized values.
It can be used for expensive-to-calculate values to ensure that the evaluation logic runs
only once and only if needed.
For example:
use sloth::Lazy; fn get_expensive_string() -> String { // do something expensive here to obtain the result, // such as read and process file contents String::from("some expensive string we got from a file or something") } fn get_expensive_number() -> i32 { // do something expensive here to calculate the result, // such as build a supercomputer and wait 7.5 million years 42 } let lazy_string = Lazy::new(get_expensive_string); let lazy_number = Lazy::new(get_expensive_number); //... let must_use_string = true; //... if must_use_string { println!("Expensive string is: {}", *lazy_string); println!("It has length: {}", lazy_string.len()); // get_expensive_string() has been called only once, // get_expensive_number() has not been called } else { println!("Expensive number is: {}", *lazy_number); println!("Its square is {}", lazy_number.pow(2)); // get_expensive_string() has not been called, // get_expensive_number() has been called only once }
The evaluated value of a mutable Lazy
can be modified:
use sloth::Lazy; let mut lazy_vec = Lazy::new(|| vec![2, -5, 6, 0]); lazy_vec.retain(|n| *n > 0); assert_eq!(*lazy_vec, vec![2, 6]);
Lazy
can be consumed and turned into its value via unwrap()
:
use sloth::Lazy; let lazy_value = Lazy::new(|| "moo"); let output = String::from("a cow goes ") + lazy_value.unwrap();
Structs
Lazy | Contains a value of some type |