33 lines
629 B
Rust
33 lines
629 B
Rust
//@ run-pass
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use std::ops::{Deref, DerefMut};
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struct CheckedDeref<T, F> {
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value: T,
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check: F
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}
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impl<F: Fn(&T) -> bool, T> Deref for CheckedDeref<T, F> {
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type Target = T;
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fn deref(&self) -> &T {
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assert!((self.check)(&self.value));
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&self.value
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}
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}
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impl<F: Fn(&T) -> bool, T> DerefMut for CheckedDeref<T, F> {
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fn deref_mut(&mut self) -> &mut T {
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assert!((self.check)(&self.value));
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&mut self.value
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}
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}
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fn main() {
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let mut v = CheckedDeref {
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value: vec![0],
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check: |v: &Vec<_>| !v.is_empty()
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};
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v.push(1);
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assert_eq!(*v, vec![0, 1]);
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}
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