sloth/
lib.rs

1//! This crate provides a generic pointer-like [`Lazy<T, Eval>`](struct.Lazy.html) struct for lazily initialized values.
2//! It can be used for expensive-to-calculate values to ensure that the evaluation logic runs
3//! only once and only if needed.
4//! 
5//! For example:
6//! ```
7//! use sloth::Lazy;
8//! 
9//! fn get_expensive_string() -> String {
10//!     // do something expensive here to obtain the result,
11//!     // such as read and process file contents
12//!     String::from("some expensive string we got from a file or something")
13//! }
14//! 
15//! fn get_expensive_number() -> i32 {
16//!     // do something expensive here to calculate the result,
17//!     // such as build a supercomputer and wait 7.5 million years
18//!     42
19//! }
20//! 
21//! let lazy_string = Lazy::new(get_expensive_string);
22//! let lazy_number = Lazy::new(get_expensive_number);
23//! 
24//! //...
25//! let must_use_string = true;
26//! //...
27//! 
28//! if must_use_string {
29//!     println!("Expensive string is: {}", *lazy_string);
30//!     println!("It has length: {}", lazy_string.len());
31//!
32//!     // get_expensive_string() has been called only once,
33//!     // get_expensive_number() has not been called
34//! } else {
35//!     println!("Expensive number is: {}", *lazy_number);
36//!     println!("Its square is {}", lazy_number.pow(2));
37//! 
38//!     // get_expensive_string() has not been called,
39//!     // get_expensive_number() has been called only once
40//! }
41//! 
42//! ```
43//! 
44//! The evaluated value of a mutable [`Lazy`](struct.Lazy.html) can be modified:
45//! ```
46//! use sloth::Lazy;
47//! 
48//! let mut lazy_vec = Lazy::new(|| vec![2, -5, 6, 0]);
49//! 
50//! lazy_vec.retain(|n| *n > 0);
51//! 
52//! assert_eq!(*lazy_vec, vec![2, 6]);
53//! ```
54//! 
55//! [`Lazy`](struct.Lazy.html) can be consumed and turned into its value via [`unwrap()`](struct.Lazy.html#method.unwrap):
56//! ```
57//! use sloth::Lazy;
58//! 
59//! let lazy_value = Lazy::new(|| "moo");
60//! 
61//! let output = String::from("a cow goes ") + lazy_value.unwrap();
62//! ```
63
64//
65// Modules
66//
67
68mod lazy;
69
70// Unit tests
71#[cfg(test)]
72#[allow(deprecated)]
73mod tests;
74
75//
76// Exports
77//
78
79pub use lazy::Lazy;
sloth/lib.rs

sloth/
lib.rs
