diff --git a/src/libcore/core.rc b/src/libcore/core.rc
index 87d0c57f09da..7253711a05f4 100644
--- a/src/libcore/core.rc
+++ b/src/libcore/core.rc
@@ -41,6 +41,8 @@ export comm, task, future;
 export extfmt;
 export tuple;
 export to_str;
+export swappable;
+export dvec, dvec_iter;
 
 // NDM seems to be necessary for resolve to work
 export vec_iter, option_iter;
@@ -165,7 +167,13 @@ mod option_iter {
 }
 mod result;
 mod to_str;
-
+mod swappable;
+mod dvec;
+#[path="iter-trait"]
+mod dvec_iter {
+    #[path = "dvec.rs"]
+    mod inst;
+}
 
 // Concurrency
 mod comm;
diff --git a/src/libcore/dvec.rs b/src/libcore/dvec.rs
new file mode 100644
index 000000000000..30dbc2a71518
--- /dev/null
+++ b/src/libcore/dvec.rs
@@ -0,0 +1,237 @@
+// Dynamic Vector
+//
+// A growable vector that makes use of unique pointers so that the
+// result can be sent between tasks and so forth.
+//
+// Note that recursive use is not permitted.
+
+import dvec_iter::extensions;
+import unsafe::reinterpret_cast;
+import ptr::{null, extensions};
+
+export dvec;
+export from_vec;
+export extensions;
+export unwrap;
+
+#[doc = "
+
+A growable, modifiable vector type that accumulates elements into a
+unique vector.
+
+# Limitations on recursive use
+
+This class works by swapping the unique vector out of the data
+structure whenever it is to be used.  Therefore, recursive use is not
+permitted.  That is, while iterating through a vector, you cannot
+access the vector in any other way or else the program will fail.  If
+you wish, you can use the `swap()` method to gain access to the raw
+vector and transform it or use it any way you like.  Eventually, we
+may permit read-only access during iteration or other use.
+
+# WARNING
+
+For maximum performance, this type is implemented using some rather
+unsafe code.  In particular, this innocent looking `[mut A]` pointer
+*may be null!*  Therefore, it is important you not reach into the
+data structure manually but instead use the provided extensions.
+
+The reason that I did not use an unsafe pointer in the structure
+itself is that I wanted to ensure that the vector would be freed when
+the dvec is dropped.  The reason that I did not use an `option<T>`
+instead of a nullable pointer is that I found experimentally that it
+becomes approximately 50% slower. This can probably be improved
+through optimization.  You can run your own experiments using
+`src/test/bench/vec-append.rs`. My own tests found that using null
+pointers achieved about 103 million pushes/second.  Using an option
+type could only produce 47 million pushes/second.
+
+"]
+type dvec<A> = {
+
+    mut data: [mut A]
+};
+
+#[doc = "Creates a new, empty dvec"]
+fn dvec<A>() -> dvec<A> {
+    {mut data: [mut]}
+}
+
+#[doc = "Creates a new dvec with the contents of a vector"]
+fn from_vec<A>(+v: [mut A]) -> dvec<A> {
+    {mut data: v}
+}
+
+#[doc = "Consumes the vector and returns its contents"]
+fn unwrap<A>(-d: dvec<A>) -> [mut A] {
+    let {data: v} <- d;
+    ret v;
+}
+
+impl private_methods<A> for dvec<A> {
+    fn check_not_borrowed() {
+        unsafe {
+            let data: *() = unsafe::reinterpret_cast(self.data);
+            if data.is_null() {
+                fail "Recursive use of dvec";
+            }
+        }
+    }
+
+    #[inline(always)]
+    fn borrow<B>(f: fn(-[mut A]) -> B) -> B {
+        unsafe {
+            let mut data = unsafe::reinterpret_cast(null::<()>());
+            data <-> self.data;
+            let data_ptr: *() = unsafe::reinterpret_cast(data);
+            if data_ptr.is_null() { fail "Recursive use of dvec"; }
+            ret f(data);
+        }
+    }
+
+    #[inline(always)]
+    fn return(-data: [mut A]) {
+        unsafe {
+            self.data <- data;
+        }
+    }
+}
+
+// In theory, most everything should work with any A, but in practice
+// almost nothing works without the copy bound due to limitations
+// around closures.
+impl extensions<A> for dvec<A> {
+    #[doc = "
+
+    Swaps out the current vector and hands it off to a user-provided
+    function `f`.  The function should transform it however is desired
+    and return a new vector to replace it with.
+
+    "]
+    fn swap(f: fn(-[mut A]) -> [mut A]) {
+        self.borrow { |v| self.return(f(v)) }
+    }
+
+    #[doc = "Returns the number of elements currently in the dvec"]
+    fn len() -> uint {
+        self.borrow { |v|
+            let l = v.len();
+            self.return(v);
+            l
+        }
+    }
+
+    #[doc = "Overwrite the current contents"]
+    fn set(+w: [mut A]) {
+        self.check_not_borrowed();
+        self.data <- w; //FIXME check for recursive use
+    }
+}
+
+impl extensions<A:copy> for dvec<A> {
+    #[doc = "Append a single item to the end of the list"]
+    fn push(t: A) {
+        self.swap { |v| v += [t]; v } // more efficient than v + [t]
+    }
+
+    #[doc = "Remove and return the last element"]
+    fn pop() -> A {
+        self.borrow { |v|
+            let result = vec::pop(v);
+            self.return(v);
+            result
+        }
+    }
+
+    #[doc = "
+        Append all elements of a vector to the end of the list
+
+        Equivalent to `append_iter()` but potentially more efficient.
+    "]
+    fn push_all(ts: [const A]/&) {
+        self.push_slice(ts, 0u, vec::len(ts));
+    }
+
+    #[doc = "
+        Appends elements from `from_idx` to `to_idx` (exclusive)
+    "]
+    fn push_slice(ts: [const A]/&, from_idx: uint, to_idx: uint) {
+        self.swap { |v|
+            let new_len = vec::len(v) + to_idx - from_idx;
+            vec::reserve(v, new_len);
+            let mut i = from_idx;
+            while i < to_idx {
+                v += [ts[i]];
+                i += 1u;
+            }
+            v
+        }
+    }
+
+    //FIXME--
+    //#[doc = "
+    //    Append all elements of an iterable.
+    //
+    //    Failure will occur if the iterable's `each()` method
+    //    attempts to access this vector.
+    //"]
+    //fn append_iter<I:iter::base<A>>(ts: I) {
+    //    self.dvec.swap { |v|
+    //        alt ts.size_hint() {
+    //          none {}
+    //          some(h) { vec::reserve(v, len(v) + h) }
+    //        }
+    //
+    //        for ts.each { |t| v = v + [t] };
+    //
+    //        v
+    //    }
+    //}
+
+    #[doc = "
+        Gets a copy of the current contents.
+
+        See `unwrap()` if you do not wish to copy the contents.
+    "]
+    fn get() -> [A] {
+        self.borrow { |v|
+            let w = vec::from_mut(copy v);
+            self.return(v);
+            w
+        }
+    }
+
+    #[doc = "Remove and return the first element"]
+    fn shift() -> A {
+        self.borrow { |v|
+            let mut v = vec::from_mut(v);
+            let result = vec::shift(v);
+            self.return(vec::to_mut(v));
+            result
+        }
+    }
+
+    #[doc = "Copy out an individual element"]
+    #[inline]
+    fn [](idx: uint) -> A {
+        self.get_elt(idx)
+    }
+
+    #[doc = "Copy out an individual element"]
+    #[inline]
+    fn get_elt(idx: uint) -> A {
+        self.check_not_borrowed();
+        ret self.data[idx];
+    }
+
+    #[doc = "Overwrites the contents of the element at `idx` with `a`"]
+    fn set_elt(idx: uint, a: A) {
+        self.check_not_borrowed();
+        self.data[idx] = a;
+    }
+
+    #[doc = "Overwrites the contents of the element at `idx` with `a`"]
+    fn grow_set_elt(idx: uint, initval: A, val: A) {
+        self.swap { |v| vec::grow_set(v, idx, initval, val); v }
+    }
+}
\ No newline at end of file
diff --git a/src/libcore/iter-trait/dvec.rs b/src/libcore/iter-trait/dvec.rs
new file mode 100644
index 000000000000..c68134153cdf
--- /dev/null
+++ b/src/libcore/iter-trait/dvec.rs
@@ -0,0 +1,16 @@
+type IMPL_T<A> = dvec::dvec<A>;
+
+#[doc = "
+Iterates through the current contents.
+
+Attempts to access this dvec during iteration will fail.
+"]
+fn EACH<A>(self: IMPL_T<A>, f: fn(A) -> bool) {
+    import dvec::extensions;
+    self.swap { |v| vec::each(v, f); v }
+}
+
+fn SIZE_HINT<A>(self: IMPL_T<A>) -> option<uint> {
+    import dvec::extensions;
+    some(self.len())
+}
diff --git a/src/libcore/swappable.rs b/src/libcore/swappable.rs
new file mode 100644
index 000000000000..5df9b2c48463
--- /dev/null
+++ b/src/libcore/swappable.rs
@@ -0,0 +1,98 @@
+export swappable;
+export unwrap;
+export methods;
+
+#[doc = "
+A value that may be swapped out temporarily while it is being processed
+and then replaced.  Swappables are most useful when working with unique
+values, which often cannot be mutated unless they are stored in the local
+stack frame to ensure memory safety.
+
+The type guarantees the invariant that the value is always \"swapped in\"
+except during the execution of the `swap()` and `with()` methods.
+"]
+type swappable<A> = {
+    mut o_t: option<A>
+};
+
+#[doc = "Create a swappable swapped in with a given initial value"]
+fn swappable<A>(+t: A) -> swappable<A> {
+    {mut o_t: some(t)}
+}
+
+#[doc = "Consumes a swappable and returns its contents without copying"]
+fn unwrap<A>(-s: swappable<A>) -> A {
+    let {o_t: o_t} <- s;
+    option::unwrap(o_t)
+}
+
+impl methods<A> for swappable<A> {
+    #[doc = "
+         Overwrites the contents of the swappable
+    "]
+    fn set(+a: A) {
+        self.o_t <- some(a);
+    }
+
+    #[doc = "
+         Invokes `f()` with the current value but replaces the
+         current value when complete.  Returns the result of `f()`.
+
+         Attempts to read or access the receiver while `f()` is executing
+         will fail dynamically.
+    "]
+    fn with<B>(f: fn(A) -> B) -> B {
+        let mut o_u = none;
+        self.swap { |t| o_u <- some(f(t)); t }
+        option::unwrap(o_u)
+    }
+
+    #[doc = "
+         Invokes `f()` with the current value and then replaces the
+         current value with the result of `f()`.
+
+         Attempts to read or access the receiver while `f()` is executing
+         will fail dynamically.
+    "]
+    fn swap(f: fn(-A) -> A) {
+        alt self.o_t {
+          none { fail "no value present---already swapped?"; }
+          some(_) {}
+        }
+
+        let mut o_t = none;
+        o_t <-> self.o_t;
+        self.o_t <- some(f(option::unwrap(o_t)));
+    }
+
+    #[doc = "True if there is a value present in this swappable"]
+    fn is_present() -> bool {
+        alt self.o_t {
+          none {false}
+          some(_) {true}
+        }
+    }
+
+    #[doc = "
+        Removes the value from the swappable.  Any further attempts
+        to use the swapabble without first invoking `set()` will fail.
+    "]
+    fn take() -> A {
+        alt self.o_t {
+          none { fail "swapped out"; }
+          some(_) {}
+        }
+
+        let mut o_t = none;
+        option::unwrap(o_t)
+    }
+}
+
+impl methods<A:copy> for swappable<A> {
+    #[doc = "
+        Copies out the contents of the swappable
+    "]
+    fn get() -> A {
+        self.o_t.get()
+    }
+}
\ No newline at end of file
diff --git a/src/test/bench/vec-append.rs b/src/test/bench/vec-append.rs
new file mode 100644
index 000000000000..a84c776f0cc6
--- /dev/null
+++ b/src/test/bench/vec-append.rs
@@ -0,0 +1,53 @@
+// A raw test of vector appending performance.
+
+use std;
+import dvec::{dvec, extensions};
+import io::writer_util;
+
+fn collect_raw(num: uint) -> [uint] {
+    let mut result = [];
+    uint::range(0u, num) { |i|
+        result += [i];
+    }
+    ret result;
+}
+
+fn collect_dvec(num: uint) -> [mut uint] {
+    let result = dvec();
+    uint::range(0u, num) { |i|
+        result.push(i);
+    }
+    ret dvec::unwrap(result);
+}
+
+fn main(args: [str]) {
+    let args = if vec::len(args) <= 1u {["", "100000"]} else {args};
+    let max = uint::from_str(args[1]).get();
+    let start = std::time::precise_time_s();
+    collect_raw(max);
+    let mid = std::time::precise_time_s();
+    collect_dvec(max);
+    let end = std::time::precise_time_s();
+
+    let raw = mid - start;
+    let dvec = end - mid;
+
+    let maxf = max as float;
+    let rawf = raw as float;
+    let dvecf = dvec as float;
+
+    io::stdout().write_str(#fmt("Raw     : %? seconds\n", raw));
+    io::stdout().write_str(#fmt("        : %f op/sec\n", maxf/rawf));
+    io::stdout().write_str(#fmt("\n"));
+    io::stdout().write_str(#fmt("Dvec    : %? seconds\n", dvec));
+    io::stdout().write_str(#fmt("        : %f op/sec\n", maxf/dvecf));
+    io::stdout().write_str(#fmt("\n"));
+
+    if dvec < raw {
+        io::stdout().write_str(#fmt("Dvec is %f%% faster than raw\n",
+                                    (rawf - dvecf) / rawf * 100.0));
+    } else {
+        io::stdout().write_str(#fmt("Raw is %f%% faster than dvec\n",
+                                    (dvecf - rawf) / dvecf * 100.0));
+    }
+}
diff --git a/src/test/run-pass/dvec-test.rs b/src/test/run-pass/dvec-test.rs
new file mode 100644
index 000000000000..01ae5e73d913
--- /dev/null
+++ b/src/test/run-pass/dvec-test.rs
@@ -0,0 +1,26 @@
+import dvec::{dvec, extensions};
+
+fn main() {
+    let d = dvec();
+    d.push(3);
+    d.push(4);
+    assert d.get() == [3, 4];
+    d.set([mut 5]);
+    d.push(6);
+    d.push(7);
+    d.push(8);
+    d.push(9);
+    d.push(10);
+    d.push_vec([11, 12, 13]);
+
+    let exp = [5, 6, 7, 8, 9, 10, 11, 12, 13];
+    assert d.get() == exp;
+    assert d.get() == exp;
+    assert d.len() == exp.len();
+
+    for d.eachi { |i, e|
+        assert e == exp[i];
+    }
+
+    assert dvec::unwrap(d) == [5, 6, 7, 8, 9, 10, 11, 12, 13];
+}
\ No newline at end of file
diff --git a/src/test/run-pass/swappable-test.rs b/src/test/run-pass/swappable-test.rs
new file mode 100644
index 000000000000..ee3446489017
--- /dev/null
+++ b/src/test/run-pass/swappable-test.rs
@@ -0,0 +1,13 @@
+import swappable::{swappable, methods};
+
+fn main() {
+    let d = swappable(3);
+    assert d.get() == 3;
+    d.set(4);
+    assert d.get() == 4;
+    d.swap { |i| i + 1 };
+    assert d.get() == 5;
+    assert d.with { |i| i + 1 } == 6;
+    assert d.get() == 5;
+    assert swappable::unwrap(d) == 5;
+}
\ No newline at end of file