deque: Implement Deque::with_capacity. Lower initial capacity to 8.
We need a reasonably small initial capacity to make Deques faster
for the common case.
diff --git a/src/libextra/deque.rs b/src/libextra/deque.rs
index 3dfc900..c537167 100644
--- a/src/libextra/deque.rs
+++ b/src/libextra/deque.rs
@@ -14,7 +14,8 @@
use std::vec;
use std::iterator::FromIterator;
-static INITIAL_CAPACITY: uint = 32u; // 2^5
+static INITIAL_CAPACITY: uint = 8u; // 2^3
+static MINIMUM_CAPACITY: uint = 2u;
#[allow(missing_doc)]
pub struct Deque<T> {
@@ -43,8 +44,13 @@
impl<T> Deque<T> {
/// Create an empty Deque
pub fn new() -> Deque<T> {
+ Deque::with_capacity(INITIAL_CAPACITY)
+ }
+
+ /// Create an empty Deque with space for at least `n` elements.
+ pub fn with_capacity(n: uint) -> Deque<T> {
Deque{nelts: 0, lo: 0,
- elts: vec::from_fn(INITIAL_CAPACITY, |_| None)}
+ elts: vec::from_fn(uint::max(MINIMUM_CAPACITY, n), |_| None)}
}
/// Return a reference to the first element in the deque
@@ -528,6 +534,16 @@
}
#[test]
+ fn test_with_capacity() {
+ let mut d = Deque::with_capacity(0);
+ d.add_back(1);
+ assert_eq!(d.len(), 1);
+ let mut d = Deque::with_capacity(50);
+ d.add_back(1);
+ assert_eq!(d.len(), 1);
+ }
+
+ #[test]
fn test_reserve() {
let mut d = Deque::new();
d.add_back(0u64);
