1 files changed, 330 insertions, 251 deletions

diff --git a/src/libstd/serialize.rs b/src/libstd/serialize.rs
index 29d108e3ac2..a5d2604b6f6 100644
--- a/src/libstd/serialize.rs
+++ b/src/libstd/serialize.rs
@@ -24,377 +24,457 @@ use treemap::{TreeMap, TreeSet};
 
 pub trait Encoder {
     // Primitive types:
-    fn emit_nil(&self);
-    fn emit_uint(&self, v: uint);
-    fn emit_u64(&self, v: u64);
-    fn emit_u32(&self, v: u32);
-    fn emit_u16(&self, v: u16);
-    fn emit_u8(&self, v: u8);
-    fn emit_int(&self, v: int);
-    fn emit_i64(&self, v: i64);
-    fn emit_i32(&self, v: i32);
-    fn emit_i16(&self, v: i16);
-    fn emit_i8(&self, v: i8);
-    fn emit_bool(&self, v: bool);
-    fn emit_float(&self, v: float);
-    fn emit_f64(&self, v: f64);
-    fn emit_f32(&self, v: f32);
-    fn emit_char(&self, v: char);
-    fn emit_str(&self, v: &str);
+    fn emit_nil(&mut self);
+    fn emit_uint(&mut self, v: uint);
+    fn emit_u64(&mut self, v: u64);
+    fn emit_u32(&mut self, v: u32);
+    fn emit_u16(&mut self, v: u16);
+    fn emit_u8(&mut self, v: u8);
+    fn emit_int(&mut self, v: int);
+    fn emit_i64(&mut self, v: i64);
+    fn emit_i32(&mut self, v: i32);
+    fn emit_i16(&mut self, v: i16);
+    fn emit_i8(&mut self, v: i8);
+    fn emit_bool(&mut self, v: bool);
+    fn emit_float(&mut self, v: float);
+    fn emit_f64(&mut self, v: f64);
+    fn emit_f32(&mut self, v: f32);
+    fn emit_char(&mut self, v: char);
+    fn emit_str(&mut self, v: &str);
 
     // Compound types:
-    fn emit_enum(&self, name: &str, f: &fn());
-
-    fn emit_enum_variant(&self, v_name: &str, v_id: uint, len: uint, f: &fn());
-    fn emit_enum_variant_arg(&self, a_idx: uint, f: &fn());
-
-    fn emit_enum_struct_variant(&self, v_name: &str, v_id: uint, len: uint, f: &fn());
-    fn emit_enum_struct_variant_field(&self, f_name: &str, f_idx: uint, f: &fn());
-
-    fn emit_struct(&self, name: &str, len: uint, f: &fn());
-    fn emit_struct_field(&self, f_name: &str, f_idx: uint, f: &fn());
-
-    fn emit_tuple(&self, len: uint, f: &fn());
-    fn emit_tuple_arg(&self, idx: uint, f: &fn());
-
-    fn emit_tuple_struct(&self, name: &str, len: uint, f: &fn());
-    fn emit_tuple_struct_arg(&self, f_idx: uint, f: &fn());
+    fn emit_enum(&mut self, name: &str, f: &fn(&mut Self));
+
+    fn emit_enum_variant(&mut self,
+                         v_name: &str,
+                         v_id: uint,
+                         len: uint,
+                         f: &fn(&mut Self));
+    fn emit_enum_variant_arg(&mut self, a_idx: uint, f: &fn(&mut Self));
+
+    fn emit_enum_struct_variant(&mut self,
+                                v_name: &str,
+                                v_id: uint,
+                                len: uint,
+                                f: &fn(&mut Self));
+    fn emit_enum_struct_variant_field(&mut self,
+                                      f_name: &str,
+                                      f_idx: uint,
+                                      f: &fn(&mut Self));
+
+    fn emit_struct(&mut self, name: &str, len: uint, f: &fn(&mut Self));
+    fn emit_struct_field(&mut self,
+                         f_name: &str,
+                         f_idx: uint,
+                         f: &fn(&mut Self));
+
+    fn emit_tuple(&mut self, len: uint, f: &fn(&mut Self));
+    fn emit_tuple_arg(&mut self, idx: uint, f: &fn(&mut Self));
+
+    fn emit_tuple_struct(&mut self, name: &str, len: uint, f: &fn(&mut Self));
+    fn emit_tuple_struct_arg(&mut self, f_idx: uint, f: &fn(&mut Self));
 
     // Specialized types:
-    fn emit_option(&self, f: &fn());
-    fn emit_option_none(&self);
-    fn emit_option_some(&self, f: &fn());
+    fn emit_option(&mut self, f: &fn(&mut Self));
+    fn emit_option_none(&mut self);
+    fn emit_option_some(&mut self, f: &fn(&mut Self));
 
-    fn emit_seq(&self, len: uint, f: &fn());
-    fn emit_seq_elt(&self, idx: uint, f: &fn());
+    fn emit_seq(&mut self, len: uint, f: &fn(this: &mut Self));
+    fn emit_seq_elt(&mut self, idx: uint, f: &fn(this: &mut Self));
 
-    fn emit_map(&self, len: uint, f: &fn());
-    fn emit_map_elt_key(&self, idx: uint, f: &fn());
-    fn emit_map_elt_val(&self, idx: uint, f: &fn());
+    fn emit_map(&mut self, len: uint, f: &fn(&mut Self));
+    fn emit_map_elt_key(&mut self, idx: uint, f: &fn(&mut Self));
+    fn emit_map_elt_val(&mut self, idx: uint, f: &fn(&mut Self));
 }
 
 pub trait Decoder {
     // Primitive types:
-    fn read_nil(&self) -> ();
-    fn read_uint(&self) -> uint;
-    fn read_u64(&self) -> u64;
-    fn read_u32(&self) -> u32;
-    fn read_u16(&self) -> u16;
-    fn read_u8(&self) -> u8;
-    fn read_int(&self) -> int;
-    fn read_i64(&self) -> i64;
-    fn read_i32(&self) -> i32;
-    fn read_i16(&self) -> i16;
-    fn read_i8(&self) -> i8;
-    fn read_bool(&self) -> bool;
-    fn read_f64(&self) -> f64;
-    fn read_f32(&self) -> f32;
-    fn read_float(&self) -> float;
-    fn read_char(&self) -> char;
-    fn read_str(&self) -> ~str;
+    fn read_nil(&mut self) -> ();
+    fn read_uint(&mut self) -> uint;
+    fn read_u64(&mut self) -> u64;
+    fn read_u32(&mut self) -> u32;
+    fn read_u16(&mut self) -> u16;
+    fn read_u8(&mut self) -> u8;
+    fn read_int(&mut self) -> int;
+    fn read_i64(&mut self) -> i64;
+    fn read_i32(&mut self) -> i32;
+    fn read_i16(&mut self) -> i16;
+    fn read_i8(&mut self) -> i8;
+    fn read_bool(&mut self) -> bool;
+    fn read_f64(&mut self) -> f64;
+    fn read_f32(&mut self) -> f32;
+    fn read_float(&mut self) -> float;
+    fn read_char(&mut self) -> char;
+    fn read_str(&mut self) -> ~str;
 
     // Compound types:
-    fn read_enum<T>(&self, name: &str, f: &fn() -> T) -> T;
-
-    fn read_enum_variant<T>(&self, names: &[&str], f: &fn(uint) -> T) -> T;
-    fn read_enum_variant_arg<T>(&self, a_idx: uint, f: &fn() -> T) -> T;
-
-    fn read_enum_struct_variant<T>(&self, names: &[&str], f: &fn(uint) -> T) -> T;
-    fn read_enum_struct_variant_field<T>(&self, &f_name: &str, f_idx: uint, f: &fn() -> T) -> T;
-
-    fn read_struct<T>(&self, s_name: &str, len: uint, f: &fn() -> T) -> T;
-    fn read_struct_field<T>(&self, f_name: &str, f_idx: uint, f: &fn() -> T) -> T;
-
-    fn read_tuple<T>(&self, f: &fn(uint) -> T) -> T;
-    fn read_tuple_arg<T>(&self, a_idx: uint, f: &fn() -> T) -> T;
-
-    fn read_tuple_struct<T>(&self, s_name: &str, f: &fn(uint) -> T) -> T;
-    fn read_tuple_struct_arg<T>(&self, a_idx: uint, f: &fn() -> T) -> T;
+    fn read_enum<T>(&mut self, name: &str, f: &fn(&mut Self) -> T) -> T;
+
+    fn read_enum_variant<T>(&mut self,
+                            names: &[&str],
+                            f: &fn(&mut Self, uint) -> T)
+                            -> T;
+    fn read_enum_variant_arg<T>(&mut self,
+                                a_idx: uint,
+                                f: &fn(&mut Self) -> T)
+                                -> T;
+
+    fn read_enum_struct_variant<T>(&mut self,
+                                   names: &[&str],
+                                   f: &fn(&mut Self, uint) -> T)
+                                   -> T;
+    fn read_enum_struct_variant_field<T>(&mut self,
+                                         &f_name: &str,
+                                         f_idx: uint,
+                                         f: &fn(&mut Self) -> T)
+                                         -> T;
+
+    fn read_struct<T>(&mut self,
+                      s_name: &str,
+                      len: uint,
+                      f: &fn(&mut Self) -> T)
+                      -> T;
+    fn read_struct_field<T>(&mut self,
+                            f_name: &str,
+                            f_idx: uint,
+                            f: &fn(&mut Self) -> T)
+                            -> T;
+
+    fn read_tuple<T>(&mut self, f: &fn(&mut Self, uint) -> T) -> T;
+    fn read_tuple_arg<T>(&mut self, a_idx: uint, f: &fn(&mut Self) -> T) -> T;
+
+    fn read_tuple_struct<T>(&mut self,
+                            s_name: &str,
+                            f: &fn(&mut Self, uint) -> T)
+                            -> T;
+    fn read_tuple_struct_arg<T>(&mut self,
+                                a_idx: uint,
+                                f: &fn(&mut Self) -> T)
+                                -> T;
 
     // Specialized types:
-    fn read_option<T>(&self, f: &fn(bool) -> T) -> T;
+    fn read_option<T>(&mut self, f: &fn(&mut Self, bool) -> T) -> T;
 
-    fn read_seq<T>(&self, f: &fn(uint) -> T) -> T;
-    fn read_seq_elt<T>(&self, idx: uint, f: &fn() -> T) -> T;
+    fn read_seq<T>(&mut self, f: &fn(&mut Self, uint) -> T) -> T;
+    fn read_seq_elt<T>(&mut self, idx: uint, f: &fn(&mut Self) -> T) -> T;
 
-    fn read_map<T>(&self, f: &fn(uint) -> T) -> T;
-    fn read_map_elt_key<T>(&self, idx: uint, f: &fn() -> T) -> T;
-    fn read_map_elt_val<T>(&self, idx: uint, f: &fn() -> T) -> T;
+    fn read_map<T>(&mut self, f: &fn(&mut Self, uint) -> T) -> T;
+    fn read_map_elt_key<T>(&mut self, idx: uint, f: &fn(&mut Self) -> T) -> T;
+    fn read_map_elt_val<T>(&mut self, idx: uint, f: &fn(&mut Self) -> T) -> T;
 }
 
 pub trait Encodable<S:Encoder> {
-    fn encode(&self, s: &S);
+    fn encode(&self, s: &mut S);
 }
 
 pub trait Decodable<D:Decoder> {
-    fn decode(d: &D) -> Self;
+    fn decode(d: &mut D) -> Self;
 }
 
 impl<S:Encoder> Encodable<S> for uint {
-    fn encode(&self, s: &S) { s.emit_uint(*self) }
+    fn encode(&self, s: &mut S) {
+        s.emit_uint(*self)
+    }
 }
 
 impl<D:Decoder> Decodable<D> for uint {
-    fn decode(d: &D) -> uint {
+    fn decode(d: &mut D) -> uint {
         d.read_uint()
     }
 }
 
 impl<S:Encoder> Encodable<S> for u8 {
-    fn encode(&self, s: &S) { s.emit_u8(*self) }
+    fn encode(&self, s: &mut S) {
+        s.emit_u8(*self)
+    }
 }
 
 impl<D:Decoder> Decodable<D> for u8 {
-    fn decode(d: &D) -> u8 {
+    fn decode(d: &mut D) -> u8 {
         d.read_u8()
     }
 }
 
 impl<S:Encoder> Encodable<S> for u16 {
-    fn encode(&self, s: &S) { s.emit_u16(*self) }
+    fn encode(&self, s: &mut S) {
+        s.emit_u16(*self)
+    }
 }
 
 impl<D:Decoder> Decodable<D> for u16 {
-    fn decode(d: &D) -> u16 {
+    fn decode(d: &mut D) -> u16 {
         d.read_u16()
     }
 }
 
 impl<S:Encoder> Encodable<S> for u32 {
-    fn encode(&self, s: &S) { s.emit_u32(*self) }
+    fn encode(&self, s: &mut S) {
+        s.emit_u32(*self)
+    }
 }
 
 impl<D:Decoder> Decodable<D> for u32 {
-    fn decode(d: &D) -> u32 {
+    fn decode(d: &mut D) -> u32 {
         d.read_u32()
     }
 }
 
 impl<S:Encoder> Encodable<S> for u64 {
-    fn encode(&self, s: &S) { s.emit_u64(*self) }
+    fn encode(&self, s: &mut S) {
+        s.emit_u64(*self)
+    }
 }
 
 impl<D:Decoder> Decodable<D> for u64 {
-    fn decode(d: &D) -> u64 {
+    fn decode(d: &mut D) -> u64 {
         d.read_u64()
     }
 }
 
 impl<S:Encoder> Encodable<S> for int {
-    fn encode(&self, s: &S) { s.emit_int(*self) }
+    fn encode(&self, s: &mut S) {
+        s.emit_int(*self)
+    }
 }
 
 impl<D:Decoder> Decodable<D> for int {
-    fn decode(d: &D) -> int {
+    fn decode(d: &mut D) -> int {
         d.read_int()
     }
 }
 
 impl<S:Encoder> Encodable<S> for i8 {
-    fn encode(&self, s: &S) { s.emit_i8(*self) }
+    fn encode(&self, s: &mut S) {
+        s.emit_i8(*self)
+    }
 }
 
 impl<D:Decoder> Decodable<D> for i8 {
-    fn decode(d: &D) -> i8 {
+    fn decode(d: &mut D) -> i8 {
         d.read_i8()
     }
 }
 
 impl<S:Encoder> Encodable<S> for i16 {
-    fn encode(&self, s: &S) { s.emit_i16(*self) }
+    fn encode(&self, s: &mut S) {
+        s.emit_i16(*self)
+    }
 }
 
 impl<D:Decoder> Decodable<D> for i16 {
-    fn decode(d: &D) -> i16 {
+    fn decode(d: &mut D) -> i16 {
         d.read_i16()
     }
 }
 
 impl<S:Encoder> Encodable<S> for i32 {
-    fn encode(&self, s: &S) { s.emit_i32(*self) }
+    fn encode(&self, s: &mut S) {
+        s.emit_i32(*self)
+    }
 }
 
 impl<D:Decoder> Decodable<D> for i32 {
-    fn decode(d: &D) -> i32 {
+    fn decode(d: &mut D) -> i32 {
         d.read_i32()
     }
 }
 
 impl<S:Encoder> Encodable<S> for i64 {
-    fn encode(&self, s: &S) { s.emit_i64(*self) }
+    fn encode(&self, s: &mut S) {
+        s.emit_i64(*self)
+    }
 }
 
 impl<D:Decoder> Decodable<D> for i64 {
-    fn decode(d: &D) -> i64 {
+    fn decode(d: &mut D) -> i64 {
         d.read_i64()
     }
 }
 
 impl<'self, S:Encoder> Encodable<S> for &'self str {
-    fn encode(&self, s: &S) { s.emit_str(*self) }
+    fn encode(&self, s: &mut S) {
+        s.emit_str(*self)
+    }
 }
 
 impl<S:Encoder> Encodable<S> for ~str {
-    fn encode(&self, s: &S) { s.emit_str(*self) }
+    fn encode(&self, s: &mut S) {
+        s.emit_str(*self)
+    }
 }
 
 impl<D:Decoder> Decodable<D> for ~str {
-    fn decode(d: &D) -> ~str {
+    fn decode(d: &mut D) -> ~str {
         d.read_str()
     }
 }
 
 impl<S:Encoder> Encodable<S> for @str {
-    fn encode(&self, s: &S) { s.emit_str(*self) }
+    fn encode(&self, s: &mut S) {
+        s.emit_str(*self)
+    }
 }
 
 impl<D:Decoder> Decodable<D> for @str {
-    fn decode(d: &D) -> @str { d.read_str().to_managed() }
+    fn decode(d: &mut D) -> @str {
+        d.read_str().to_managed()
+    }
 }
 
 impl<S:Encoder> Encodable<S> for float {
-    fn encode(&self, s: &S) { s.emit_float(*self) }
+    fn encode(&self, s: &mut S) {
+        s.emit_float(*self)
+    }
 }
 
 impl<D:Decoder> Decodable<D> for float {
-    fn decode(d: &D) -> float {
+    fn decode(d: &mut D) -> float {
         d.read_float()
     }
 }
 
 impl<S:Encoder> Encodable<S> for f32 {
-    fn encode(&self, s: &S) { s.emit_f32(*self) }
+    fn encode(&self, s: &mut S) {
+        s.emit_f32(*self)
+    }
 }
 
 impl<D:Decoder> Decodable<D> for f32 {
-    fn decode(d: &D) -> f32 {
-        d.read_f32() }
+    fn decode(d: &mut D) -> f32 {
+        d.read_f32()
+    }
 }
 
 impl<S:Encoder> Encodable<S> for f64 {
-    fn encode(&self, s: &S) { s.emit_f64(*self) }
+    fn encode(&self, s: &mut S) {
+        s.emit_f64(*self)
+    }
 }
 
 impl<D:Decoder> Decodable<D> for f64 {
-    fn decode(d: &D) -> f64 {
+    fn decode(d: &mut D) -> f64 {
         d.read_f64()
     }
 }
 
 impl<S:Encoder> Encodable<S> for bool {
-    fn encode(&self, s: &S) { s.emit_bool(*self) }
+    fn encode(&self, s: &mut S) {
+        s.emit_bool(*self)
+    }
 }
 
 impl<D:Decoder> Decodable<D> for bool {
-    fn decode(d: &D) -> bool {
+    fn decode(d: &mut D) -> bool {
         d.read_bool()
     }
 }
 
 impl<S:Encoder> Encodable<S> for () {
-    fn encode(&self, s: &S) { s.emit_nil() }
+    fn encode(&self, s: &mut S) {
+        s.emit_nil()
+    }
 }
 
 impl<D:Decoder> Decodable<D> for () {
-    fn decode(d: &D) -> () {
+    fn decode(d: &mut D) -> () {
         d.read_nil()
     }
 }
 
 impl<'self, S:Encoder,T:Encodable<S>> Encodable<S> for &'self T {
-    fn encode(&self, s: &S) {
+    fn encode(&self, s: &mut S) {
         (**self).encode(s)
     }
 }
 
 impl<S:Encoder,T:Encodable<S>> Encodable<S> for ~T {
-    fn encode(&self, s: &S) {
+    fn encode(&self, s: &mut S) {
         (**self).encode(s)
     }
 }
 
 impl<D:Decoder,T:Decodable<D>> Decodable<D> for ~T {
-    fn decode(d: &D) -> ~T {
+    fn decode(d: &mut D) -> ~T {
         ~Decodable::decode(d)
     }
 }
 
 impl<S:Encoder,T:Encodable<S>> Encodable<S> for @T {
-    fn encode(&self, s: &S) {
+    fn encode(&self, s: &mut S) {
         (**self).encode(s)
     }
 }
 
 impl<D:Decoder,T:Decodable<D>> Decodable<D> for @T {
-    fn decode(d: &D) -> @T {
+    fn decode(d: &mut D) -> @T {
         @Decodable::decode(d)
     }
 }
 
 impl<'self, S:Encoder,T:Encodable<S>> Encodable<S> for &'self [T] {
-    fn encode(&self, s: &S) {
-        do s.emit_seq(self.len()) {
+    fn encode(&self, s: &mut S) {
+        do s.emit_seq(self.len()) |s| {
             for self.eachi |i, e| {
-                s.emit_seq_elt(i, || e.encode(s))
+                s.emit_seq_elt(i, |s| e.encode(s))
             }
         }
     }
 }
 
 impl<S:Encoder,T:Encodable<S>> Encodable<S> for ~[T] {
-    fn encode(&self, s: &S) {
-        do s.emit_seq(self.len()) {
+    fn encode(&self, s: &mut S) {
+        do s.emit_seq(self.len()) |s| {
             for self.eachi |i, e| {
-                s.emit_seq_elt(i, || e.encode(s))
+                s.emit_seq_elt(i, |s| e.encode(s))
             }
         }
     }
 }
 
 impl<D:Decoder,T:Decodable<D>> Decodable<D> for ~[T] {
-    fn decode(d: &D) -> ~[T] {
-        do d.read_seq |len| {
+    fn decode(d: &mut D) -> ~[T] {
+        do d.read_seq |d, len| {
             do vec::from_fn(len) |i| {
-                d.read_seq_elt(i, || Decodable::decode(d))
+                d.read_seq_elt(i, |d| Decodable::decode(d))
             }
         }
     }
 }
 
 impl<S:Encoder,T:Encodable<S>> Encodable<S> for @[T] {
-    fn encode(&self, s: &S) {
-        do s.emit_seq(self.len()) {
+    fn encode(&self, s: &mut S) {
+        do s.emit_seq(self.len()) |s| {
             for self.eachi |i, e| {
-                s.emit_seq_elt(i, || e.encode(s))
+                s.emit_seq_elt(i, |s| e.encode(s))
             }
         }
     }
 }
 
 impl<D:Decoder,T:Decodable<D>> Decodable<D> for @[T] {
-    fn decode(d: &D) -> @[T] {
-        do d.read_seq |len| {
+    fn decode(d: &mut D) -> @[T] {
+        do d.read_seq |d, len| {
             do at_vec::from_fn(len) |i| {
-                d.read_seq_elt(i, || Decodable::decode(d))
+                d.read_seq_elt(i, |d| Decodable::decode(d))
             }
         }
     }
 }
 
 impl<S:Encoder,T:Encodable<S>> Encodable<S> for Option<T> {
-    fn encode(&self, s: &S) {
-        do s.emit_option {
+    fn encode(&self, s: &mut S) {
+        do s.emit_option |s| {
             match *self {
                 None => s.emit_option_none(),
-                Some(ref v) => s.emit_option_some(|| v.encode(s)),
+                Some(ref v) => s.emit_option_some(|s| v.encode(s)),
             }
         }
     }
 }
 
 impl<D:Decoder,T:Decodable<D>> Decodable<D> for Option<T> {
-    fn decode(d: &D) -> Option<T> {
-        do d.read_option |b| {
+    fn decode(d: &mut D) -> Option<T> {
+        do d.read_option |d, b| {
             if b {
                 Some(Decodable::decode(d))
             } else {
@@ -405,12 +485,12 @@ impl<D:Decoder,T:Decodable<D>> Decodable<D> for Option<T> {
 }
 
 impl<S:Encoder,T0:Encodable<S>,T1:Encodable<S>> Encodable<S> for (T0, T1) {
-    fn encode(&self, s: &S) {
+    fn encode(&self, s: &mut S) {
         match *self {
             (ref t0, ref t1) => {
-                do s.emit_seq(2) {
-                    s.emit_seq_elt(0, || t0.encode(s));
-                    s.emit_seq_elt(1, || t1.encode(s));
+                do s.emit_seq(2) |s| {
+                    s.emit_seq_elt(0, |s| t0.encode(s));
+                    s.emit_seq_elt(1, |s| t1.encode(s));
                 }
             }
         }
@@ -418,12 +498,12 @@ impl<S:Encoder,T0:Encodable<S>,T1:Encodable<S>> Encodable<S> for (T0, T1) {
 }
 
 impl<D:Decoder,T0:Decodable<D>,T1:Decodable<D>> Decodable<D> for (T0, T1) {
-    fn decode(d: &D) -> (T0, T1) {
-        do d.read_seq |len| {
+    fn decode(d: &mut D) -> (T0, T1) {
+        do d.read_seq |d, len| {
             assert!(len == 2);
             (
-                d.read_seq_elt(0, || Decodable::decode(d)),
-                d.read_seq_elt(1, || Decodable::decode(d))
+                d.read_seq_elt(0, |d| Decodable::decode(d)),
+                d.read_seq_elt(1, |d| Decodable::decode(d))
             )
         }
     }
@@ -435,13 +515,13 @@ impl<
     T1: Encodable<S>,
     T2: Encodable<S>
 > Encodable<S> for (T0, T1, T2) {
-    fn encode(&self, s: &S) {
+    fn encode(&self, s: &mut S) {
         match *self {
             (ref t0, ref t1, ref t2) => {
-                do s.emit_seq(3) {
-                    s.emit_seq_elt(0, || t0.encode(s));
-                    s.emit_seq_elt(1, || t1.encode(s));
-                    s.emit_seq_elt(2, || t2.encode(s));
+                do s.emit_seq(3) |s| {
+                    s.emit_seq_elt(0, |s| t0.encode(s));
+                    s.emit_seq_elt(1, |s| t1.encode(s));
+                    s.emit_seq_elt(2, |s| t2.encode(s));
                 }
             }
         }
@@ -454,13 +534,13 @@ impl<
     T1: Decodable<D>,
     T2: Decodable<D>
 > Decodable<D> for (T0, T1, T2) {
-    fn decode(d: &D) -> (T0, T1, T2) {
-        do d.read_seq |len| {
+    fn decode(d: &mut D) -> (T0, T1, T2) {
+        do d.read_seq |d, len| {
             assert!(len == 3);
             (
-                d.read_seq_elt(0, || Decodable::decode(d)),
-                d.read_seq_elt(1, || Decodable::decode(d)),
-                d.read_seq_elt(2, || Decodable::decode(d))
+                d.read_seq_elt(0, |d| Decodable::decode(d)),
+                d.read_seq_elt(1, |d| Decodable::decode(d)),
+                d.read_seq_elt(2, |d| Decodable::decode(d))
             )
         }
     }
@@ -473,14 +553,14 @@ impl<
     T2: Encodable<S>,
     T3: Encodable<S>
 > Encodable<S> for (T0, T1, T2, T3) {
-    fn encode(&self, s: &S) {
+    fn encode(&self, s: &mut S) {
         match *self {
             (ref t0, ref t1, ref t2, ref t3) => {
-                do s.emit_seq(4) {
-                    s.emit_seq_elt(0, || t0.encode(s));
-                    s.emit_seq_elt(1, || t1.encode(s));
-                    s.emit_seq_elt(2, || t2.encode(s));
-                    s.emit_seq_elt(3, || t3.encode(s));
+                do s.emit_seq(4) |s| {
+                    s.emit_seq_elt(0, |s| t0.encode(s));
+                    s.emit_seq_elt(1, |s| t1.encode(s));
+                    s.emit_seq_elt(2, |s| t2.encode(s));
+                    s.emit_seq_elt(3, |s| t3.encode(s));
                 }
             }
         }
@@ -494,14 +574,14 @@ impl<
     T2: Decodable<D>,
     T3: Decodable<D>
 > Decodable<D> for (T0, T1, T2, T3) {
-    fn decode(d: &D) -> (T0, T1, T2, T3) {
-        do d.read_seq |len| {
+    fn decode(d: &mut D) -> (T0, T1, T2, T3) {
+        do d.read_seq |d, len| {
             assert!(len == 4);
             (
-                d.read_seq_elt(0, || Decodable::decode(d)),
-                d.read_seq_elt(1, || Decodable::decode(d)),
-                d.read_seq_elt(2, || Decodable::decode(d)),
-                d.read_seq_elt(3, || Decodable::decode(d))
+                d.read_seq_elt(0, |d| Decodable::decode(d)),
+                d.read_seq_elt(1, |d| Decodable::decode(d)),
+                d.read_seq_elt(2, |d| Decodable::decode(d)),
+                d.read_seq_elt(3, |d| Decodable::decode(d))
             )
         }
     }
@@ -515,15 +595,15 @@ impl<
     T3: Encodable<S>,
     T4: Encodable<S>
 > Encodable<S> for (T0, T1, T2, T3, T4) {
-    fn encode(&self, s: &S) {
+    fn encode(&self, s: &mut S) {
         match *self {
             (ref t0, ref t1, ref t2, ref t3, ref t4) => {
-                do s.emit_seq(5) {
-                    s.emit_seq_elt(0, || t0.encode(s));
-                    s.emit_seq_elt(1, || t1.encode(s));
-                    s.emit_seq_elt(2, || t2.encode(s));
-                    s.emit_seq_elt(3, || t3.encode(s));
-                    s.emit_seq_elt(4, || t4.encode(s));
+                do s.emit_seq(5) |s| {
+                    s.emit_seq_elt(0, |s| t0.encode(s));
+                    s.emit_seq_elt(1, |s| t1.encode(s));
+                    s.emit_seq_elt(2, |s| t2.encode(s));
+                    s.emit_seq_elt(3, |s| t3.encode(s));
+                    s.emit_seq_elt(4, |s| t4.encode(s));
                 }
             }
         }
@@ -538,16 +618,15 @@ impl<
     T3: Decodable<D>,
     T4: Decodable<D>
 > Decodable<D> for (T0, T1, T2, T3, T4) {
-    fn decode(d: &D)
-      -> (T0, T1, T2, T3, T4) {
-        do d.read_seq |len| {
+    fn decode(d: &mut D) -> (T0, T1, T2, T3, T4) {
+        do d.read_seq |d, len| {
             assert!(len == 5);
             (
-                d.read_seq_elt(0, || Decodable::decode(d)),
-                d.read_seq_elt(1, || Decodable::decode(d)),
-                d.read_seq_elt(2, || Decodable::decode(d)),
-                d.read_seq_elt(3, || Decodable::decode(d)),
-                d.read_seq_elt(4, || Decodable::decode(d))
+                d.read_seq_elt(0, |d| Decodable::decode(d)),
+                d.read_seq_elt(1, |d| Decodable::decode(d)),
+                d.read_seq_elt(2, |d| Decodable::decode(d)),
+                d.read_seq_elt(3, |d| Decodable::decode(d)),
+                d.read_seq_elt(4, |d| Decodable::decode(d))
             )
         }
     }
@@ -557,11 +636,11 @@ impl<
     S: Encoder,
     T: Encodable<S> + Copy
 > Encodable<S> for @mut DList<T> {
-    fn encode(&self, s: &S) {
-        do s.emit_seq(self.size) {
+    fn encode(&self, s: &mut S) {
+        do s.emit_seq(self.size) |s| {
             let mut i = 0;
             for self.each |e| {
-                s.emit_seq_elt(i, || e.encode(s));
+                s.emit_seq_elt(i, |s| e.encode(s));
                 i += 1;
             }
         }
@@ -569,11 +648,11 @@ impl<
 }
 
 impl<D:Decoder,T:Decodable<D>> Decodable<D> for @mut DList<T> {
-    fn decode(d: &D) -> @mut DList<T> {
+    fn decode(d: &mut D) -> @mut DList<T> {
         let list = DList();
-        do d.read_seq |len| {
+        do d.read_seq |d, len| {
             for uint::range(0, len) |i| {
-                list.push(d.read_seq_elt(i, || Decodable::decode(d)));
+                list.push(d.read_seq_elt(i, |d| Decodable::decode(d)));
             }
         }
         list
@@ -584,21 +663,21 @@ impl<
     S: Encoder,
     T: Encodable<S>
 > Encodable<S> for Deque<T> {
-    fn encode(&self, s: &S) {
-        do s.emit_seq(self.len()) {
+    fn encode(&self, s: &mut S) {
+        do s.emit_seq(self.len()) |s| {
             for self.eachi |i, e| {
-                s.emit_seq_elt(i, || e.encode(s));
+                s.emit_seq_elt(i, |s| e.encode(s));
             }
         }
     }
 }
 
 impl<D:Decoder,T:Decodable<D>> Decodable<D> for Deque<T> {
-    fn decode(d: &D) -> Deque<T> {
+    fn decode(d: &mut D) -> Deque<T> {
         let mut deque = Deque::new();
-        do d.read_seq |len| {
+        do d.read_seq |d, len| {
             for uint::range(0, len) |i| {
-                deque.add_back(d.read_seq_elt(i, || Decodable::decode(d)));
+                deque.add_back(d.read_seq_elt(i, |d| Decodable::decode(d)));
             }
         }
         deque
@@ -610,12 +689,12 @@ impl<
     K: Encodable<E> + Hash + IterBytes + Eq,
     V: Encodable<E>
 > Encodable<E> for HashMap<K, V> {
-    fn encode(&self, e: &E) {
-        do e.emit_map(self.len()) {
+    fn encode(&self, e: &mut E) {
+        do e.emit_map(self.len()) |e| {
             let mut i = 0;
             for self.each |key, val| {
-                e.emit_map_elt_key(i, || key.encode(e));
-                e.emit_map_elt_val(i, || val.encode(e));
+                e.emit_map_elt_key(i, |e| key.encode(e));
+                e.emit_map_elt_val(i, |e| val.encode(e));
                 i += 1;
             }
         }
@@ -627,12 +706,12 @@ impl<
     K: Decodable<D> + Hash + IterBytes + Eq,
     V: Decodable<D>
 > Decodable<D> for HashMap<K, V> {
-    fn decode(d: &D) -> HashMap<K, V> {
-        do d.read_map |len| {
+    fn decode(d: &mut D) -> HashMap<K, V> {
+        do d.read_map |d, len| {
             let mut map = HashMap::with_capacity(len);
             for uint::range(0, len) |i| {
-                let key = d.read_map_elt_key(i, || Decodable::decode(d));
-                let val = d.read_map_elt_val(i, || Decodable::decode(d));
+                let key = d.read_map_elt_key(i, |d| Decodable::decode(d));
+                let val = d.read_map_elt_val(i, |d| Decodable::decode(d));
                 map.insert(key, val);
             }
             map
@@ -644,11 +723,11 @@ impl<
     S: Encoder,
     T: Encodable<S> + Hash + IterBytes + Eq
 > Encodable<S> for HashSet<T> {
-    fn encode(&self, s: &S) {
-        do s.emit_seq(self.len()) {
+    fn encode(&self, s: &mut S) {
+        do s.emit_seq(self.len()) |s| {
             let mut i = 0;
             for self.each |e| {
-                s.emit_seq_elt(i, || e.encode(s));
+                s.emit_seq_elt(i, |s| e.encode(s));
                 i += 1;
             }
         }
@@ -659,11 +738,11 @@ impl<
     D: Decoder,
     T: Decodable<D> + Hash + IterBytes + Eq
 > Decodable<D> for HashSet<T> {
-    fn decode(d: &D) -> HashSet<T> {
-        do d.read_seq |len| {
+    fn decode(d: &mut D) -> HashSet<T> {
+        do d.read_seq |d, len| {
             let mut set = HashSet::with_capacity(len);
             for uint::range(0, len) |i| {
-                set.insert(d.read_seq_elt(i, || Decodable::decode(d)));
+                set.insert(d.read_seq_elt(i, |d| Decodable::decode(d)));
             }
             set
         }
@@ -674,12 +753,12 @@ impl<
     E: Encoder,
     V: Encodable<E>
 > Encodable<E> for TrieMap<V> {
-    fn encode(&self, e: &E) {
-        do e.emit_map(self.len()) {
+    fn encode(&self, e: &mut E) {
+        do e.emit_map(self.len()) |e| {
             let mut i = 0;
             for self.each |key, val| {
-                e.emit_map_elt_key(i, || key.encode(e));
-                e.emit_map_elt_val(i, || val.encode(e));
+                e.emit_map_elt_key(i, |e| key.encode(e));
+                e.emit_map_elt_val(i, |e| val.encode(e));
                 i += 1;
             }
         }
@@ -690,12 +769,12 @@ impl<
     D: Decoder,
     V: Decodable<D>
 > Decodable<D> for TrieMap<V> {
-    fn decode(d: &D) -> TrieMap<V> {
-        do d.read_map |len| {
+    fn decode(d: &mut D) -> TrieMap<V> {
+        do d.read_map |d, len| {
             let mut map = TrieMap::new();
             for uint::range(0, len) |i| {
-                let key = d.read_map_elt_key(i, || Decodable::decode(d));
-                let val = d.read_map_elt_val(i, || Decodable::decode(d));
+                let key = d.read_map_elt_key(i, |d| Decodable::decode(d));
+                let val = d.read_map_elt_val(i, |d| Decodable::decode(d));
                 map.insert(key, val);
             }
             map
@@ -704,11 +783,11 @@ impl<
 }
 
 impl<S: Encoder> Encodable<S> for TrieSet {
-    fn encode(&self, s: &S) {
-        do s.emit_seq(self.len()) {
+    fn encode(&self, s: &mut S) {
+        do s.emit_seq(self.len()) |s| {
             let mut i = 0;
             for self.each |e| {
-                s.emit_seq_elt(i, || e.encode(s));
+                s.emit_seq_elt(i, |s| e.encode(s));
                 i += 1;
             }
         }
@@ -716,11 +795,11 @@ impl<S: Encoder> Encodable<S> for TrieSet {
 }
 
 impl<D: Decoder> Decodable<D> for TrieSet {
-    fn decode(d: &D) -> TrieSet {
-        do d.read_seq |len| {
+    fn decode(d: &mut D) -> TrieSet {
+        do d.read_seq |d, len| {
             let mut set = TrieSet::new();
             for uint::range(0, len) |i| {
-                set.insert(d.read_seq_elt(i, || Decodable::decode(d)));
+                set.insert(d.read_seq_elt(i, |d| Decodable::decode(d)));
             }
             set
         }
@@ -732,12 +811,12 @@ impl<
     K: Encodable<E> + Eq + TotalOrd,
     V: Encodable<E> + Eq
 > Encodable<E> for TreeMap<K, V> {
-    fn encode(&self, e: &E) {
-        do e.emit_map(self.len()) {
+    fn encode(&self, e: &mut E) {
+        do e.emit_map(self.len()) |e| {
             let mut i = 0;
             for self.each |key, val| {
-                e.emit_map_elt_key(i, || key.encode(e));
-                e.emit_map_elt_val(i, || val.encode(e));
+                e.emit_map_elt_key(i, |e| key.encode(e));
+                e.emit_map_elt_val(i, |e| val.encode(e));
                 i += 1;
             }
         }
@@ -749,12 +828,12 @@ impl<
     K: Decodable<D> + Eq + TotalOrd,
     V: Decodable<D> + Eq
 > Decodable<D> for TreeMap<K, V> {
-    fn decode(d: &D) -> TreeMap<K, V> {
-        do d.read_map |len| {
+    fn decode(d: &mut D) -> TreeMap<K, V> {
+        do d.read_map |d, len| {
             let mut map = TreeMap::new();
             for uint::range(0, len) |i| {
-                let key = d.read_map_elt_key(i, || Decodable::decode(d));
-                let val = d.read_map_elt_val(i, || Decodable::decode(d));
+                let key = d.read_map_elt_key(i, |d| Decodable::decode(d));
+                let val = d.read_map_elt_val(i, |d| Decodable::decode(d));
                 map.insert(key, val);
             }
             map
@@ -766,11 +845,11 @@ impl<
     S: Encoder,
     T: Encodable<S> + Eq + TotalOrd
 > Encodable<S> for TreeSet<T> {
-    fn encode(&self, s: &S) {
-        do s.emit_seq(self.len()) {
+    fn encode(&self, s: &mut S) {
+        do s.emit_seq(self.len()) |s| {
             let mut i = 0;
             for self.each |e| {
-                s.emit_seq_elt(i, || e.encode(s));
+                s.emit_seq_elt(i, |s| e.encode(s));
                 i += 1;
             }
         }
@@ -781,11 +860,11 @@ impl<
     D: Decoder,
     T: Decodable<D> + Eq + TotalOrd
 > Decodable<D> for TreeSet<T> {
-    fn decode(d: &D) -> TreeSet<T> {
-        do d.read_seq |len| {
+    fn decode(d: &mut D) -> TreeSet<T> {
+        do d.read_seq |d, len| {
             let mut set = TreeSet::new();
             for uint::range(0, len) |i| {
-                set.insert(d.read_seq_elt(i, || Decodable::decode(d)));
+                set.insert(d.read_seq_elt(i, |d| Decodable::decode(d)));
             }
             set
         }
@@ -798,15 +877,15 @@ impl<
 // In some cases, these should eventually be coded as traits.
 
 pub trait EncoderHelpers {
-    fn emit_from_vec<T>(&self, v: &[T], f: &fn(v: &T));
+    fn emit_from_vec<T>(&mut self, v: &[T], f: &fn(&mut Self, v: &T));
 }
 
 impl<S:Encoder> EncoderHelpers for S {
-    fn emit_from_vec<T>(&self, v: &[T], f: &fn(v: &T)) {
-        do self.emit_seq(v.len()) {
+    fn emit_from_vec<T>(&mut self, v: &[T], f: &fn(&mut S, &T)) {
+        do self.emit_seq(v.len()) |this| {
             for v.eachi |i, e| {
-                do self.emit_seq_elt(i) {
-                    f(e)
+                do this.emit_seq_elt(i) |this| {
+                    f(this, e)
                 }
             }
         }
@@ -814,14 +893,14 @@ impl<S:Encoder> EncoderHelpers for S {
 }
 
 pub trait DecoderHelpers {
-    fn read_to_vec<T>(&self, f: &fn() -> T) -> ~[T];
+    fn read_to_vec<T>(&mut self, f: &fn(&mut Self) -> T) -> ~[T];
 }
 
 impl<D:Decoder> DecoderHelpers for D {
-    fn read_to_vec<T>(&self, f: &fn() -> T) -> ~[T] {
-        do self.read_seq |len| {
+    fn read_to_vec<T>(&mut self, f: &fn(&mut D) -> T) -> ~[T] {
+        do self.read_seq |this, len| {
             do vec::from_fn(len) |i| {
-                self.read_seq_elt(i, || f())
+                this.read_seq_elt(i, |this| f(this))
             }
         }
     }