Struct sloth::Lazy

pub struct Lazy<T, Eval> where
    Eval: FnOnce() -> T,  { /* fields omitted */ }

Represents a value of type T, lazily evaluated using a parameterless function or a closure (FnOnce() -> T) passed to Lazy::new().

The value within may be referenced using value_ref() or value_mut() methods. For types implementing Copy, a copy of the contained value may be obtained using value().

The evaluator function will not be called more than once. If none of value(), value_ref() and value_mut() methods are used, the evaluator function will never be called at all.

Examples

Lazily converting a string to upper case:

use sloth::Lazy;
 
let some_str = "the quick brown fox jumps over the lazy dog";
let lazy_upper_str = Lazy::new(|| some_str.to_uppercase());
 
assert_eq!(
    *lazy_upper_str.value_ref(),
    "THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG"
);

Regardless of how many times the value is accessed, the evaluator function is only called once:

use sloth::Lazy;
 
let mut evaluator_called_times = 0;
 
let lazy_value = Lazy::new(|| {
    evaluator_called_times += 1;
    25
});
 
assert_eq!(lazy_value.value(), 25);
 
let another_value = lazy_value.value() + lazy_value.value();
 
assert_eq!(evaluator_called_times, 1);

Methods

impl<T, Eval> Lazy<T, Eval> where
    Eval: FnOnce() -> T, 

pub fn new(evaluator: Eval) -> Self

pub fn value_ref(&self) -> Ref<T>

pub fn value_mut(&mut self) -> RefMut<T>

impl<T, Eval> Lazy<T, Eval> where
    T: Copy,
    Eval: FnOnce() -> T, 

pub fn value(&self) -> T