[−][src]Crate sloth
This crate provides a generic Lazy<T, Eval>
wrapper struct for lazy initialization.
It can be used for expensive-to-calculate T
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_i32() -> 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_i32 = Lazy::new(get_expensive_i32); //... let must_use_string = true; //... if must_use_string { println!("Expensive string is: {}", *lazy_string.value_ref()); println!("It has length: {}", (*lazy_string.value_ref()).len()); // get_expensive_string() has been called only once, // get_expensive_i32() has not been called at all } else { println!("Expensive int is: {}", lazy_i32.value()); println!("It is{} divisible by 6", if lazy_i32.value() % 6 == 0 { "" } else { " not" }); // get_expensive_string() has not been called, // get_expensive_i32() has been called only once }
Structs
Lazy | Represents a value of some type |