diff --git a/src/libcore/dvec.rs b/src/libcore/dvec.rs
index ec396f474a7c..f9bb58380b2d 100644
--- a/src/libcore/dvec.rs
+++ b/src/libcore/dvec.rs
@@ -46,28 +46,32 @@ export unwrap;
  * pointers achieved about 103 million pushes/second.  Using an option
  * type could only produce 47 million pushes/second.
  */
-type dvec<A> = {
+type dvec_<A> = {
     mut data: ~[mut A]
 };
 
+enum dvec<A> {
+    dvec_(dvec_<A>)
+}
+
 /// Creates a new, empty dvec
 fn dvec<A>() -> dvec<A> {
-    {mut data: ~[mut]}
+    dvec_({mut data: ~[mut]})
 }
 
 /// Creates a new dvec with a single element
 fn from_elem<A>(+e: A) -> dvec<A> {
-    {mut data: ~[mut e]}
+    dvec_({mut data: ~[mut e]})
 }
 
 /// Creates a new dvec with the contents of a vector
 fn from_vec<A>(+v: ~[mut A]) -> dvec<A> {
-    {mut data: v}
+    dvec_({mut data: v})
 }
 
 /// Consumes the vector and returns its contents
 fn unwrap<A>(-d: dvec<A>) -> ~[mut A] {
-    let {data: v} <- d;
+    let dvec_({data: v}) <- d;
     ret v;
 }
 
diff --git a/src/libcore/iter-trait.rs b/src/libcore/iter-trait.rs
index 02c32a1bf0db..80b81753af81 100644
--- a/src/libcore/iter-trait.rs
+++ b/src/libcore/iter-trait.rs
@@ -21,7 +21,7 @@ impl extensions<A> of iter::base_iter<A> for IMPL_T<A> {
     }
 }
 
-impl extensions<A:copy> for IMPL_T<A> {
+impl extensions<A:copy> of iter::copyable_iter<A> for IMPL_T<A> {
     fn filter_to_vec(pred: fn(A) -> bool) -> ~[A] {
         iter::filter_to_vec(self, pred)
     }
diff --git a/src/libcore/iter.rs b/src/libcore/iter.rs
index 55d47cfe75d3..31e47d19c8f6 100644
--- a/src/libcore/iter.rs
+++ b/src/libcore/iter.rs
@@ -7,6 +7,15 @@ iface times {
     fn times(it: fn() -> bool);
 }
 
+trait copyable_iter<A:copy> {
+    fn filter_to_vec(pred: fn(A) -> bool) -> ~[A];
+    fn map_to_vec<B>(op: fn(A) -> B) -> ~[B];
+    fn to_vec() -> ~[A];
+    fn min() -> A;
+    fn max() -> A;
+    fn find(p: fn(A) -> bool) -> option<A>;
+}
+
 fn eachi<A,IA:base_iter<A>>(self: IA, blk: fn(uint, A) -> bool) {
     let mut i = 0u;
     for self.each |a| {
diff --git a/src/libcore/pipes.rs b/src/libcore/pipes.rs
index 658d59a43757..2b17a8a78747 100644
--- a/src/libcore/pipes.rs
+++ b/src/libcore/pipes.rs
@@ -11,16 +11,24 @@ enum state {
     terminated
 }
 
-type packet_header = {
+type packet_header_ = {
     mut state: state,
     mut blocked_task: option<*rust_task>,
 };
 
-type packet<T: send> = {
+enum packet_header {
+    packet_header_(packet_header_)
+}
+
+type packet_<T:send> = {
     header: packet_header,
     mut payload: option<T>
 };
 
+enum packet<T:send> {
+    packet_(packet_<T>)
+}
+
 fn packet<T: send>() -> *packet<T> unsafe {
     let p: *packet<T> = unsafe::transmute(~{
         header: {
@@ -428,8 +436,17 @@ proto! streamp {
     }
 }
 
-type chan<T:send> = { mut endp: option<streamp::client::open<T>> };
-type port<T:send> = { mut endp: option<streamp::server::open<T>> };
+type chan_<T:send> = { mut endp: option<streamp::client::open<T>> };
+
+enum chan<T:send> {
+    chan_(chan_<T>)
+}
+
+type port_<T:send> = { mut endp: option<streamp::server::open<T>> };
+
+enum port<T:send> {
+    port_(port_<T>)
+}
 
 fn stream<T:send>() -> (chan<T>, port<T>) {
     let (c, s) = streamp::init();
@@ -439,7 +456,7 @@ fn stream<T:send>() -> (chan<T>, port<T>) {
          unsafe { let y <- *ptr::addr_of(x); y }]
     ];
 
-    ({ mut endp: some(c) }, { mut endp: some(s) })
+    (chan_({ mut endp: some(c) }), port_({ mut endp: some(s) }))
 }
 
 impl chan<T: send> for chan<T> {
diff --git a/src/libcore/ptr.rs b/src/libcore/ptr.rs
index 704c0fcaf4b7..97795103f52d 100644
--- a/src/libcore/ptr.rs
+++ b/src/libcore/ptr.rs
@@ -123,8 +123,13 @@ unsafe fn memset<T>(dst: *mut T, c: int, count: uint)  {
     libc_::memset(dst as *c_void, c as libc::c_int, n as size_t);
 }
 
+trait ptr {
+    pure fn is_null() -> bool;
+    pure fn is_not_null() -> bool;
+}
+
 /// Extension methods for pointers
-impl extensions<T> for *T {
+impl extensions<T> of ptr for *T {
     /// Returns true if the pointer is equal to the null pointer.
     pure fn is_null() -> bool { is_null(self) }
 
diff --git a/src/libcore/str.rs b/src/libcore/str.rs
index 2d9d97979097..cd1724765639 100644
--- a/src/libcore/str.rs
+++ b/src/libcore/str.rs
@@ -1882,8 +1882,15 @@ mod unsafe {
 
 }
 
+trait unique_str {
+    fn trim() -> self;
+    fn trim_left() -> self;
+    fn trim_right() -> self;
+    pure fn +(rhs: str/&) -> self;
+}
+
 /// Extension methods for strings
-impl extensions for str {
+impl extensions of unique_str for str {
     /// Returns a string with leading and trailing whitespace removed
     #[inline]
     fn trim() -> str { trim(self) }
@@ -1901,8 +1908,35 @@ impl extensions for str {
     }
 }
 
+trait str_slice {
+    fn all(it: fn(char) -> bool) -> bool;
+    fn any(it: fn(char) -> bool) -> bool;
+    fn contains(needle: str/&a) -> bool;
+    fn contains_char(needle: char) -> bool;
+    fn each(it: fn(u8) -> bool);
+    fn eachi(it: fn(uint, u8) -> bool);
+    fn each_char(it: fn(char) -> bool);
+    fn each_chari(it: fn(uint, char) -> bool);
+    fn ends_with(needle: str/&) -> bool;
+    fn is_empty() -> bool;
+    fn is_not_empty() -> bool;
+    fn is_whitespace() -> bool;
+    fn is_alphanumeric() -> bool;
+    pure fn len() -> uint;
+    fn slice(begin: uint, end: uint) -> str;
+    fn split(sepfn: fn(char) -> bool) -> ~[str];
+    fn split_char(sep: char) -> ~[str];
+    fn split_str(sep: str/&a) -> ~[str];
+    fn starts_with(needle: str/&a) -> bool;
+    fn substr(begin: uint, n: uint) -> str;
+    fn to_lower() -> str;
+    fn to_upper() -> str;
+    fn escape_default() -> str;
+    fn escape_unicode() -> str;
+}
+
 /// Extension methods for strings
-impl extensions/& for str/& {
+impl extensions/& of str_slice for str/& {
     /**
      * Return true if a predicate matches all characters or if the string
      * contains no characters
diff --git a/src/libcore/vec.rs b/src/libcore/vec.rs
index eb3d52edc24e..a4bc4d66999a 100644
--- a/src/libcore/vec.rs
+++ b/src/libcore/vec.rs
@@ -1181,22 +1181,32 @@ pure fn unpack_mut_slice<T,U>(s: &[mut T],
     }
 }
 
-impl extensions<T: copy> for ~[T] {
+trait vec_concat<T> {
+    pure fn +(rhs: &[const T]) -> self;
+}
+
+impl extensions<T: copy> of vec_concat<T> for ~[T] {
     #[inline(always)]
     pure fn +(rhs: &[const T]) -> ~[T] {
         append(self, rhs)
     }
 }
 
-impl extensions<T: copy> for ~[mut T] {
+impl extensions<T: copy> of vec_concat<T> for ~[mut T] {
     #[inline(always)]
     pure fn +(rhs: &[const T]) -> ~[mut T] {
         append_mut(self, rhs)
     }
 }
 
+trait const_vector {
+    pure fn is_empty() -> bool;
+    pure fn is_not_empty() -> bool;
+    pure fn len() -> uint;
+}
+
 /// Extension methods for vectors
-impl extensions/&<T> for &[const T] {
+impl extensions/&<T> of const_vector for &[const T] {
     /// Returns true if a vector contains no elements
     #[inline]
     pure fn is_empty() -> bool { is_empty(self) }
@@ -1208,8 +1218,16 @@ impl extensions/&<T> for &[const T] {
     pure fn len() -> uint { len(self) }
 }
 
+trait copyable_vector<T> {
+    pure fn head() -> T;
+    pure fn init() -> ~[T];
+    pure fn last() -> T;
+    pure fn slice(start: uint, end: uint) -> ~[T];
+    pure fn tail() -> ~[T];
+}
+
 /// Extension methods for vectors
-impl extensions/&<T: copy> for &[const T] {
+impl extensions/&<T: copy> of copyable_vector<T> for &[const T] {
     /// Returns the first element of a vector
     #[inline]
     pure fn head() -> T { head(self) }
@@ -1227,8 +1245,26 @@ impl extensions/&<T: copy> for &[const T] {
     pure fn tail() -> ~[T] { tail(self) }
 }
 
+trait immutable_vector/&<T> {
+    pure fn foldr<U: copy>(z: U, p: fn(T, U) -> U) -> U;
+    pure fn iter(f: fn(T));
+    pure fn iteri(f: fn(uint, T));
+    pure fn position(f: fn(T) -> bool) -> option<uint>;
+    pure fn position_elem(x: T) -> option<uint>;
+    pure fn riter(f: fn(T));
+    pure fn riteri(f: fn(uint, T));
+    pure fn rposition(f: fn(T) -> bool) -> option<uint>;
+    pure fn rposition_elem(x: T) -> option<uint>;
+    pure fn map<U>(f: fn(T) -> U) -> ~[U];
+    pure fn mapi<U>(f: fn(uint, T) -> U) -> ~[U];
+    fn map_r<U>(f: fn(x: &self.T) -> U) -> ~[U];
+    pure fn alli(f: fn(uint, T) -> bool) -> bool;
+    pure fn flat_map<U>(f: fn(T) -> ~[U]) -> ~[U];
+    pure fn filter_map<U: copy>(f: fn(T) -> option<U>) -> ~[U];
+}
+
 /// Extension methods for vectors
-impl extensions/&<T> for &[T] {
+impl extensions/&<T> of immutable_vector<T> for &[T] {
     /// Reduce a vector from right to left
     #[inline]
     pure fn foldr<U: copy>(z: U, p: fn(T, U) -> U) -> U { foldr(self, z, p) }
@@ -1336,8 +1372,14 @@ impl extensions/&<T> for &[T] {
     }
 }
 
+trait immutable_copyable_vector<T> {
+    pure fn filter(f: fn(T) -> bool) -> ~[T];
+    pure fn find(f: fn(T) -> bool) -> option<T>;
+    pure fn rfind(f: fn(T) -> bool) -> option<T>;
+}
+
 /// Extension methods for vectors
-impl extensions/&<T: copy> for &[T] {
+impl extensions/&<T: copy> of immutable_copyable_vector<T> for &[T] {
     /**
      * Construct a new vector from the elements of a vector for which some
      * predicate holds.
@@ -1510,7 +1552,16 @@ impl extensions/&<A> of iter::base_iter<A> for &[const A] {
     fn contains(x: A) -> bool { iter::contains(self, x) }
     fn count(x: A) -> uint { iter::count(self, x) }
 }
-impl extensions/&<A:copy> for &[const A] {
+
+trait iter_trait_extensions<A> {
+    fn filter_to_vec(pred: fn(A) -> bool) -> ~[A];
+    fn map_to_vec<B>(op: fn(A) -> B) -> ~[B];
+    fn to_vec() -> ~[A];
+    fn min() -> A;
+    fn max() -> A;
+}
+
+impl extensions/&<A:copy> of iter_trait_extensions<A> for &[const A] {
     fn filter_to_vec(pred: fn(A) -> bool) -> ~[A] {
         iter::filter_to_vec(self, pred)
     }