syntax: add the OwnedSlice vector wrapper.

This is a stand-in until we have a saner `~[T]` type (i.e. a proper
owned slice). It's a library version of what `~[T]` will be, i.e. an
owned pointer and a length.

src/libsyntax/lib.rs

@@ -49,6 +49,7 @@ pub mod syntax {
     pub use parse;
 }
 
+pub mod owned_slice;
 pub mod opt_vec;
 pub mod attr;
 pub mod diagnostic;

src/libsyntax/owned_slice.rs

@@ -0,0 +1,142 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::default::Default;
+use std::hash::Hash;
+use std::{cast, mem, raw, ptr, slice};
+use serialize::{Encodable, Decodable, Encoder, Decoder};
+
+/// A non-growable owned slice. This would preferably become `~[T]`
+/// under DST.
+#[unsafe_no_drop_flag] // data is set to null on destruction
+pub struct OwnedSlice<T> {
+    /// null iff len == 0
+    priv data: *mut T,
+    priv len: uint,
+}
+
+#[unsafe_destructor]
+impl<T> Drop for OwnedSlice<T> {
+    fn drop(&mut self) {
+        if self.data.is_null() { return }
+
+        // extract the vector
+        let v = mem::replace(self, OwnedSlice::empty());
+        // free via the Vec destructor
+        v.into_vec();
+    }
+}
+
+impl<T> OwnedSlice<T> {
+    pub fn empty() -> OwnedSlice<T> {
+        OwnedSlice  { data: ptr::mut_null(), len: 0 }
+    }
+
+    #[inline(never)]
+    pub fn from_vec(mut v: Vec<T>) -> OwnedSlice<T> {
+        let len = v.len();
+
+        if len == 0 {
+            OwnedSlice::empty()
+        } else {
+            let p = v.as_mut_ptr();
+            // we own the allocation now
+            unsafe {cast::forget(v)}
+
+            OwnedSlice { data: p, len: len }
+        }
+    }
+
+    #[inline(never)]
+    pub fn into_vec(self) -> Vec<T> {
+        // null is ok, because len == 0 in that case, as required by Vec.
+        unsafe {
+            let ret = Vec::from_raw_parts(self.len, self.len, self.data);
+            // the vector owns the allocation now
+            cast::forget(self);
+            ret
+        }
+    }
+
+    pub fn as_slice<'a>(&'a self) -> &'a [T] {
+        static PTR_MARKER: u8 = 0;
+        let ptr = if self.data.is_null() {
+            // length zero, i.e. this will never be read as a T.
+            &PTR_MARKER as *u8 as *T
+        } else {
+            self.data as *T
+        };
+
+        let slice: &[T] = unsafe {cast::transmute(raw::Slice {
+            data: ptr,
+            len: self.len
+        })};
+
+        slice
+    }
+
+    pub fn get<'a>(&'a self, i: uint) -> &'a T {
+        self.as_slice().get(i).expect("OwnedSlice: index out of bounds")
+    }
+
+    pub fn iter<'r>(&'r self) -> slice::Items<'r, T> {
+        self.as_slice().iter()
+    }
+
+    pub fn map<U>(&self, f: |&T| -> U) -> OwnedSlice<U> {
+        self.iter().map(f).collect()
+    }
+}
+
+impl<T> Default for OwnedSlice<T> {
+    fn default() -> OwnedSlice<T> {
+        OwnedSlice::empty()
+    }
+}
+
+impl<T: Clone> Clone for OwnedSlice<T> {
+    fn clone(&self) -> OwnedSlice<T> {
+        OwnedSlice::from_vec(Vec::from_slice(self.as_slice()))
+    }
+}
+
+impl<S: Writer, T: Hash<S>> Hash<S> for OwnedSlice<T> {
+    fn hash(&self, state: &mut S) {
+        self.as_slice().hash(state)
+    }
+}
+
+impl<T: Eq> Eq for OwnedSlice<T> {
+    fn eq(&self, other: &OwnedSlice<T>) -> bool {
+        self.as_slice() == other.as_slice()
+    }
+}
+
+impl<T> Container for OwnedSlice<T> {
+    fn len(&self) -> uint { self.len }
+}
+
+impl<T> FromIterator<T> for OwnedSlice<T> {
+    fn from_iterator<I: Iterator<T>>(iter: &mut I) -> OwnedSlice<T> {
+        OwnedSlice::from_vec(iter.collect())
+    }
+}
+
+impl<S: Encoder, T: Encodable<S>> Encodable<S> for OwnedSlice<T> {
+    fn encode(&self, s: &mut S) {
+       self.as_slice().encode(s)
+    }
+}
+
+impl<D: Decoder, T: Decodable<D>> Decodable<D> for OwnedSlice<T> {
+    fn decode(d: &mut D) -> OwnedSlice<T> {
+        OwnedSlice::from_vec(Decodable::decode(d))
+    }
+}