39 lines
771 B
Rust
39 lines
771 B
Rust
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use std::{
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fmt::{Display, Formatter, self},
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};
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pub struct LazyString<'f, F>
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where F: Fn() -> String + 'f
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{
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source: F,
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_lifetime: std::marker::PhantomData<dyn Fn() + 'f>,
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}
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impl<'f, F> LazyString<'f, F>
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where F: Fn() -> String + 'f
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{
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pub fn new(source: F) -> Self {
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LazyString {
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source,
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_lifetime: Default::default(),
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}
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}
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}
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impl<'f, F> Display for LazyString<'f, F>
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where F: Fn() -> String + 'f
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{
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fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
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let s = (self.source)();
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Display::fmt(&s, fmt)
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}
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}
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#[test]
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fn test_lazy_string() {
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let i = 10;
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let lzstr = LazyString::new(|| format!("the value is {}", i));
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assert_eq!(lzstr.to_string(), "the value is 10");
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}
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