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use std::collections::TryReserveError;
pub trait TrySetCapacity {
fn try_set_capacity(&mut self, capacity: usize) -> Result<(), TryReserveError>;
}
pub trait TrySetCapacityExact {
fn try_set_capacity_exact(&mut self, capacity: usize) -> Result<(), TryReserveError>;
}
impl<T> TrySetCapacity for Vec<T> {
fn try_set_capacity(&mut self, capacity: usize) -> Result<(), TryReserveError> {
let additional = capacity.saturating_sub(self.len());
self.try_reserve(additional)
}
}
impl<T> TrySetCapacityExact for Vec<T> {
fn try_set_capacity_exact(&mut self, capacity: usize) -> Result<(), TryReserveError> {
let additional = capacity.saturating_sub(self.len());
self.try_reserve_exact(additional)
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_try_set_capacity() {
// Constructing uses exact capacity
let mut v = vec![1, 2, 3];
assert_eq!(v.capacity(), 3);
// Set capacity to 5, but it will double to 6
v.try_set_capacity(5).unwrap();
assert_eq!(v.capacity(), 6);
// Setting capacity again does nothing
v.try_set_capacity(5).unwrap();
assert_eq!(v.capacity(), 6);
// Fill up to capacity
v.extend([4, 5, 6]);
assert_eq!(v.capacity(), 6);
// Push over capacity will double it
v.push(7);
assert_eq!(v.capacity(), 12);
// Set capacity to 100
v.try_set_capacity(100).unwrap();
assert_eq!(v.capacity(), 100);
// Capacity will never shrink
v.try_set_capacity(5).unwrap();
assert_eq!(v.capacity(), 100);
}
#[test]
fn test_try_set_capacity_exact() {
// Constructing uses exact capacity
let mut v = vec![1, 2, 3];
assert_eq!(v.capacity(), 3);
// Set capacity to exactly 5
v.try_set_capacity_exact(5).unwrap();
assert_eq!(v.capacity(), 5);
// Setting capacity again does nothing
v.try_set_capacity_exact(5).unwrap();
assert_eq!(v.capacity(), 5);
// Fill up to capacity
v.extend([4, 5]);
assert_eq!(v.capacity(), 5);
// Push over capacity will double it
v.push(6);
assert_eq!(v.capacity(), 10);
// Set capacity to exactly 100
v.try_set_capacity_exact(100).unwrap();
assert_eq!(v.capacity(), 100);
// Capacity will never shrink
v.try_set_capacity_exact(5).unwrap();
assert_eq!(v.capacity(), 100);
}
}
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