blob: 359f9b7842da3775cc735bd35e326231ff9a2ee7 [file] [log] [blame]
/// A vector type optimized for cases where this size is usually 0 (cf. `SmallVector`).
/// The `Option<Box<..>>` wrapping allows us to represent a zero sized vector with `None`,
/// which uses only a single (null) pointer.
#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
pub struct ThinVec<T>(Option<Box<Vec<T>>>);
impl<T> ThinVec<T> {
pub fn new() -> Self {
ThinVec(None)
}
}
impl<T> From<Vec<T>> for ThinVec<T> {
fn from(vec: Vec<T>) -> Self {
if vec.is_empty() {
ThinVec(None)
} else {
ThinVec(Some(Box::new(vec)))
}
}
}
impl<T> Into<Vec<T>> for ThinVec<T> {
fn into(self) -> Vec<T> {
match self {
ThinVec(None) => Vec::new(),
ThinVec(Some(vec)) => *vec,
}
}
}
impl<T> ::std::ops::Deref for ThinVec<T> {
type Target = [T];
fn deref(&self) -> &[T] {
match *self {
ThinVec(None) => &[],
ThinVec(Some(ref vec)) => vec,
}
}
}
impl<T> Extend<T> for ThinVec<T> {
fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
match *self {
ThinVec(Some(ref mut vec)) => vec.extend(iter),
ThinVec(None) => *self = iter.into_iter().collect::<Vec<_>>().into(),
}
}
}