Use void for the unreachable serializers

Cargo.toml

@@ -14,3 +14,4 @@ test = false
 [dependencies]
 serde = "0.9.2"
 url = "1.0.0"
+void = "1.0.2"

src/lib.rs

@@ -3,6 +3,7 @@
 #[macro_use]
 extern crate serde;
 extern crate url;
+extern crate void;
 
 pub mod de;
 pub mod ser;

src/ser/mod.rs

@@ -4,12 +4,12 @@ mod key;
 mod pair;
 mod part;
 mod value;
+mod void;
 
 use serde::ser;
 use std::borrow::Cow;
 use std::error;
 use std::fmt;
-use std::marker::PhantomData;
 use std::str;
 use url::form_urlencoded::Serializer as UrlEncodedSerializer;
 use url::form_urlencoded::Target as UrlEncodedTarget;
@@ -102,21 +102,21 @@ pub struct SeqSerializer<'output, Target: 'output + UrlEncodedTarget> {
 ///
 /// Never instantiated, tuples are not supported at top-level.
 pub struct TupleSerializer<'output, T: 'output + UrlEncodedTarget> {
-    _marker: PhantomData<&'output T>,
+    inner: void::VoidSerializer<&'output mut UrlEncodedSerializer<T>>,
 }
 
 /// Tuple struct serializer.
 ///
 /// Never instantiated, tuple structs are not supported.
 pub struct TupleStructSerializer<'output, T: 'output + UrlEncodedTarget> {
-    _marker: PhantomData<&'output T>,
+    inner: void::VoidSerializer<&'output mut UrlEncodedSerializer<T>>,
 }
 
 /// Tuple variant serializer.
 ///
 /// Never instantiated, tuple variants are not supported.
 pub struct TupleVariantSerializer<'output, T: 'output + UrlEncodedTarget> {
-    _marker: PhantomData<&'output T>,
+    inner: void::VoidSerializer<&'output mut UrlEncodedSerializer<T>>,
 }
 
 /// Map serializer.
@@ -134,7 +134,7 @@ pub struct StructSerializer<'output, Target: 'output + UrlEncodedTarget> {
 ///
 /// Never instantiated, struct variants are not supported.
 pub struct StructVariantSerializer<'output, T: 'output + UrlEncodedTarget> {
-    _marker: PhantomData<&'output T>,
+    inner: void::VoidSerializer<&'output mut UrlEncodedSerializer<T>>,
 }
 
 impl<'output, Target> ser::Serializer for Serializer<'output, Target>
@@ -368,13 +368,13 @@ impl<'output, Target> ser::SerializeTuple for TupleSerializer<'output, Target>
     type Error = Error;
 
     fn serialize_element<T: ?Sized + ser::Serialize>(&mut self,
-                                                     _value: &T)
+                                                     value: &T)
                                                      -> Result<(), Error> {
-        unreachable!()
+        self.inner.serialize_element(value)
     }
 
     fn end(self) -> Result<Self::Ok, Error> {
-        unreachable!()
+        self.inner.end()
     }
 }
 
@@ -386,13 +386,13 @@ impl<'output, Target> ser::SerializeTupleStruct
     type Error = Error;
 
     fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
-                                                   _value: &T)
+                                                   value: &T)
                                                    -> Result<(), Error> {
-        unreachable!()
+        self.inner.serialize_field(value)
     }
 
     fn end(self) -> Result<Self::Ok, Error> {
-        unreachable!()
+        self.inner.end()
     }
 }
 
@@ -404,13 +404,13 @@ impl<'output, Target> ser::SerializeTupleVariant
     type Error = Error;
 
     fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
-                                                   _value: &T)
+                                                   value: &T)
                                                    -> Result<(), Error> {
-        unreachable!()
+        self.inner.serialize_field(value)
     }
 
     fn end(self) -> Result<Self::Ok, Error> {
-        unreachable!()
+        self.inner.end()
     }
 }
 
@@ -488,14 +488,14 @@ impl<'output, Target> ser::SerializeStructVariant
     type Error = Error;
 
     fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
-                                                   _key: &'static str,
+                                                   key: &'static str,
-                                                   _value: &T)
+                                                   value: &T)
                                                    -> Result<(), Error> {
-        unreachable!()
+        self.inner.serialize_field(key, value)
     }
 
     fn end(self) -> Result<Self::Ok, Error> {
-        unreachable!()
+        self.inner.end()
     }
 }
 

src/ser/pair.rs

@@ -2,6 +2,7 @@ use ser::Error;
 use ser::key::KeySink;
 use ser::part::PartSerializer;
 use ser::value::ValueSink;
+use ser::void::VoidSerializer;
 use serde::ser;
 use std::borrow::Cow;
 use std::mem;
@@ -29,13 +30,13 @@ impl<'target, Target> ser::Serializer for PairSerializer<'target, Target>
 {
     type Ok = ();
     type Error = Error;
-    type SerializeSeq = Self;
+    type SerializeSeq = VoidSerializer<()>;
     type SerializeTuple = Self;
-    type SerializeTupleStruct = Self;
+    type SerializeTupleStruct = VoidSerializer<()>;
-    type SerializeTupleVariant = Self;
+    type SerializeTupleVariant = VoidSerializer<()>;
-    type SerializeMap = Self;
+    type SerializeMap = VoidSerializer<()>;
-    type SerializeStruct = Self;
+    type SerializeStruct = VoidSerializer<()>;
-    type SerializeStructVariant = Self;
+    type SerializeStructVariant = VoidSerializer<()>;
 
     fn serialize_bool(self, _v: bool) -> Result<(), Error> {
         Err(Error::unsupported_pair())
@@ -137,11 +138,15 @@ impl<'target, Target> ser::Serializer for PairSerializer<'target, Target>
         value.serialize(self)
     }
 
-    fn serialize_seq(self, _len: Option<usize>) -> Result<Self, Error> {
+    fn serialize_seq(self,
+                     _len: Option<usize>)
+                     -> Result<VoidSerializer<()>, Error> {
         Err(Error::unsupported_pair())
     }
 
-    fn serialize_seq_fixed_size(self, _len: usize) -> Result<Self, Error> {
+    fn serialize_seq_fixed_size(self,
+                                _len: usize)
+                                -> Result<VoidSerializer<()>, Error> {
         Err(Error::unsupported_pair())
     }
 
@@ -156,7 +161,7 @@ impl<'target, Target> ser::Serializer for PairSerializer<'target, Target>
     fn serialize_tuple_struct(self,
                               _name: &'static str,
                               _len: usize)
-                              -> Result<Self, Error> {
+                              -> Result<VoidSerializer<()>, Error> {
         Err(Error::unsupported_pair())
     }
 
@@ -165,18 +170,20 @@ impl<'target, Target> ser::Serializer for PairSerializer<'target, Target>
                                _variant_index: usize,
                                _variant: &'static str,
                                _len: usize)
-                               -> Result<Self, Error> {
+                               -> Result<VoidSerializer<()>, Error> {
         Err(Error::unsupported_pair())
     }
 
-    fn serialize_map(self, _len: Option<usize>) -> Result<Self, Error> {
+    fn serialize_map(self,
+                     _len: Option<usize>)
+                     -> Result<VoidSerializer<()>, Error> {
         Err(Error::unsupported_pair())
     }
 
     fn serialize_struct(self,
                         _name: &'static str,
                         _len: usize)
-                        -> Result<Self, Error> {
+                        -> Result<VoidSerializer<()>, Error> {
         Err(Error::unsupported_pair())
     }
 
@@ -185,28 +192,11 @@ impl<'target, Target> ser::Serializer for PairSerializer<'target, Target>
                                 _variant_index: usize,
                                 _variant: &'static str,
                                 _len: usize)
-                                -> Result<Self, Error> {
+                                -> Result<VoidSerializer<()>, Error> {
         Err(Error::unsupported_pair())
     }
 }
 
-impl<'target, Target> ser::SerializeSeq for PairSerializer<'target, Target>
-    where Target: 'target + UrlEncodedTarget,
-{
-    type Ok = ();
-    type Error = Error;
-
-    fn serialize_element<T: ?Sized + ser::Serialize>(&mut self,
-                                                     _value: &T)
-                                                     -> Result<(), Error> {
-        unreachable!()
-    }
-
-    fn end(self) -> Result<(), Error> {
-        unreachable!()
-    }
-}
-
 impl<'target, Target> ser::SerializeTuple for PairSerializer<'target, Target>
     where Target: 'target + UrlEncodedTarget,
 {
@@ -251,102 +241,6 @@ impl<'target, Target> ser::SerializeTuple for PairSerializer<'target, Target>
     }
 }
 
-impl<'target, Target> ser::SerializeTupleStruct
-    for PairSerializer<'target, Target>
-    where Target: 'target + UrlEncodedTarget,
-{
-    type Ok = ();
-    type Error = Error;
-
-    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
-                                                   _value: &T)
-                                                   -> Result<(), Error> {
-        unreachable!()
-    }
-
-    fn end(self) -> Result<(), Error> {
-        unreachable!()
-    }
-}
-
-impl<'target, Target> ser::SerializeTupleVariant
-    for PairSerializer<'target, Target>
-    where Target: 'target + UrlEncodedTarget,
-{
-    type Ok = ();
-    type Error = Error;
-
-    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
-                                                   _value: &T)
-                                                   -> Result<(), Error> {
-        unreachable!()
-    }
-
-    fn end(self) -> Result<(), Error> {
-        unreachable!()
-    }
-}
-
-impl<'target, Target> ser::SerializeMap for PairSerializer<'target, Target>
-    where Target: 'target + UrlEncodedTarget,
-{
-    type Ok = ();
-    type Error = Error;
-
-    fn serialize_key<T: ?Sized + ser::Serialize>(&mut self,
-                                                 _key: &T)
-                                                 -> Result<(), Error> {
-        unreachable!()
-    }
-
-    fn serialize_value<T: ?Sized + ser::Serialize>(&mut self,
-                                                   _value: &T)
-                                                   -> Result<(), Error> {
-        unreachable!()
-    }
-
-    fn end(self) -> Result<(), Error> {
-        unreachable!()
-    }
-}
-
-impl<'target, Target> ser::SerializeStruct for PairSerializer<'target, Target>
-    where Target: 'target + UrlEncodedTarget,
-{
-    type Ok = ();
-    type Error = Error;
-
-    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
-                                                   _key: &'static str,
-                                                   _value: &T)
-                                                   -> Result<(), Error> {
-        unreachable!()
-    }
-
-    fn end(self) -> Result<(), Error> {
-        unreachable!()
-    }
-}
-
-impl<'target, Target> ser::SerializeStructVariant
-    for PairSerializer<'target, Target>
-    where Target: 'target + UrlEncodedTarget,
-{
-    type Ok = ();
-    type Error = Error;
-
-    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
-                                                   _key: &'static str,
-                                                   _value: &T)
-                                                   -> Result<(), Error> {
-        unreachable!()
-    }
-
-    fn end(self) -> Result<(), Error> {
-        unreachable!()
-    }
-}
-
 enum PairState {
     WaitingForKey,
     WaitingForValue { key: Cow<'static, str> },

src/ser/part.rs

@@ -1,4 +1,5 @@
 use ser::Error;
+use ser::void::VoidSerializer;
 use serde::ser;
 use std::str;
 
@@ -36,13 +37,13 @@ pub trait Sink: Sized {
 impl<S: Sink> ser::Serializer for PartSerializer<S> {
     type Ok = S::Ok;
     type Error = Error;
-    type SerializeSeq = Self;
+    type SerializeSeq = VoidSerializer<S::Ok>;
-    type SerializeTuple = Self;
+    type SerializeTuple = VoidSerializer<S::Ok>;
-    type SerializeTupleStruct = Self;
+    type SerializeTupleStruct = VoidSerializer<S::Ok>;
-    type SerializeTupleVariant = Self;
+    type SerializeTupleVariant = VoidSerializer<S::Ok>;
-    type SerializeMap = Self;
+    type SerializeMap = VoidSerializer<S::Ok>;
-    type SerializeStruct = Self;
+    type SerializeStruct = VoidSerializer<S::Ok>;
-    type SerializeStructVariant = Self;
+    type SerializeStructVariant = VoidSerializer<S::Ok>;
 
     fn serialize_bool(self, v: bool) -> Result<S::Ok, Error> {
         self.sink.serialize_bool(v)
@@ -147,165 +148,62 @@ impl<S: Sink> ser::Serializer for PartSerializer<S> {
         self.sink.serialize_some(value)
     }
 
-    fn serialize_seq(self, _len: Option<usize>) -> Result<Self, Error> {
+    fn serialize_seq(self,
+                     _len: Option<usize>)
+                     -> Result<Self::SerializeSeq, Error> {
         Err(self.sink.unsupported())
     }
 
 
-    fn serialize_seq_fixed_size(self, _len: usize) -> Result<Self, Error> {
+    fn serialize_seq_fixed_size(self,
+                                _len: usize)
+                                -> Result<Self::SerializeSeq, Error> {
         Err(self.sink.unsupported())
     }
 
-    fn serialize_tuple(self, _len: usize) -> Result<Self, Error> {
+    fn serialize_tuple(self,
+                       _len: usize)
+                       -> Result<Self::SerializeTuple, Error> {
         Err(self.sink.unsupported())
     }
 
     fn serialize_tuple_struct(self,
                               _name: &'static str,
                               _len: usize)
-                              -> Result<Self, Error> {
+                              -> Result<Self::SerializeTuple, Error> {
         Err(self.sink.unsupported())
     }
 
-    fn serialize_tuple_variant(self,
+    fn serialize_tuple_variant
-                               _name: &'static str,
+        (self,
-                               _variant_index: usize,
+         _name: &'static str,
-                               _variant: &'static str,
+         _variant_index: usize,
-                               _len: usize)
+         _variant: &'static str,
-                               -> Result<Self, Error> {
+         _len: usize)
+         -> Result<Self::SerializeTupleVariant, Error> {
         Err(self.sink.unsupported())
     }
 
-    fn serialize_map(self, _len: Option<usize>) -> Result<Self, Error> {
+    fn serialize_map(self,
+                     _len: Option<usize>)
+                     -> Result<Self::SerializeMap, Error> {
         Err(self.sink.unsupported())
     }
 
     fn serialize_struct(self,
                         _name: &'static str,
                         _len: usize)
-                        -> Result<Self, Error> {
+                        -> Result<Self::SerializeStruct, Error> {
         Err(self.sink.unsupported())
     }
 
-    fn serialize_struct_variant(self,
+    fn serialize_struct_variant
-                                _name: &'static str,
+        (self,
-                                _variant_index: usize,
+         _name: &'static str,
-                                _variant: &'static str,
+         _variant_index: usize,
-                                _len: usize)
+         _variant: &'static str,
-                                -> Result<Self, Error> {
+         _len: usize)
+         -> Result<Self::SerializeStructVariant, Error> {
         Err(self.sink.unsupported())
     }
 }
-
-impl<S: Sink> ser::SerializeSeq for PartSerializer<S> {
-    type Ok = S::Ok;
-    type Error = Error;
-
-    fn serialize_element<T: ?Sized + ser::Serialize>(&mut self,
-                                                     _value: &T)
-                                                     -> Result<(), Error> {
-        unreachable!()
-    }
-
-    fn end(self) -> Result<S::Ok, Error> {
-        unreachable!()
-    }
-}
-
-impl<S: Sink> ser::SerializeTuple for PartSerializer<S> {
-    type Ok = S::Ok;
-    type Error = Error;
-
-    fn serialize_element<T: ?Sized + ser::Serialize>(&mut self,
-                                                     _value: &T)
-                                                     -> Result<(), Error> {
-        unreachable!()
-    }
-
-    fn end(self) -> Result<S::Ok, Error> {
-        unreachable!()
-    }
-}
-
-impl<S: Sink> ser::SerializeTupleStruct for PartSerializer<S> {
-    type Ok = S::Ok;
-    type Error = Error;
-
-    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
-                                                   _value: &T)
-                                                   -> Result<(), Error> {
-        unreachable!()
-    }
-
-    fn end(self) -> Result<S::Ok, Error> {
-        unreachable!()
-    }
-}
-
-impl<S: Sink> ser::SerializeTupleVariant for PartSerializer<S> {
-    type Ok = S::Ok;
-    type Error = Error;
-
-    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
-                                                   _value: &T)
-                                                   -> Result<(), Error> {
-        unreachable!()
-    }
-
-    fn end(self) -> Result<S::Ok, Error> {
-        unreachable!()
-    }
-}
-
-impl<S: Sink> ser::SerializeMap for PartSerializer<S> {
-    type Ok = S::Ok;
-    type Error = Error;
-
-    fn serialize_key<T: ?Sized + ser::Serialize>(&mut self,
-                                                 _key: &T)
-                                                 -> Result<(), Error> {
-        unreachable!()
-    }
-
-    fn serialize_value<T: ?Sized + ser::Serialize>(&mut self,
-                                                   _value: &T)
-                                                   -> Result<(), Error> {
-        unreachable!()
-    }
-
-    fn end(self) -> Result<S::Ok, Error> {
-        unreachable!()
-    }
-}
-
-impl<S: Sink> ser::SerializeStruct for PartSerializer<S> {
-    type Ok = S::Ok;
-    type Error = Error;
-
-    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
-                                                   _key: &'static str,
-                                                   _value: &T)
-                                                   -> Result<(), Error> {
-        unreachable!()
-    }
-
-    fn end(self) -> Result<S::Ok, Error> {
-        unreachable!()
-    }
-}
-
-impl<S: Sink> ser::SerializeStructVariant for PartSerializer<S> {
-    type Ok = S::Ok;
-    type Error = Error;
-
-    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
-                                                   _key: &'static str,
-                                                   _value: &T)
-                                                   -> Result<(), Error> {
-        unreachable!()
-    }
-
-    fn end(self) -> Result<S::Ok, Error> {
-        unreachable!()
-    }
-}

src/ser/void.rs

@@ -0,0 +1,122 @@
+use ser::Error;
+use serde::ser;
+use std::marker::PhantomData;
+use void;
+
+pub struct VoidSerializer<Ok> {
+    void: void::Void,
+    _marker: PhantomData<Ok>,
+}
+
+impl<Ok> ser::SerializeSeq for VoidSerializer<Ok> {
+    type Ok = Ok;
+    type Error = Error;
+
+    fn serialize_element<T: ?Sized + ser::Serialize>(&mut self,
+                                                     _value: &T)
+                                                     -> Result<(), Error> {
+        void::unreachable(self.void)
+    }
+
+    fn end(self) -> Result<Ok, Error> {
+        void::unreachable(self.void)
+    }
+}
+
+impl<Ok> ser::SerializeTuple for VoidSerializer<Ok> {
+    type Ok = Ok;
+    type Error = Error;
+
+    fn serialize_element<T: ?Sized + ser::Serialize>(&mut self,
+                                                     _value: &T)
+                                                     -> Result<(), Error> {
+        void::unreachable(self.void)
+    }
+
+    fn end(self) -> Result<Ok, Error> {
+        void::unreachable(self.void)
+    }
+}
+
+impl<Ok> ser::SerializeTupleStruct for VoidSerializer<Ok> {
+    type Ok = Ok;
+    type Error = Error;
+
+    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
+                                                   _value: &T)
+                                                   -> Result<(), Error> {
+        void::unreachable(self.void)
+    }
+
+    fn end(self) -> Result<Ok, Error> {
+        void::unreachable(self.void)
+    }
+}
+
+impl<Ok> ser::SerializeTupleVariant for VoidSerializer<Ok> {
+    type Ok = Ok;
+    type Error = Error;
+
+    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
+                                                   _value: &T)
+                                                   -> Result<(), Error> {
+        void::unreachable(self.void)
+    }
+
+    fn end(self) -> Result<Ok, Error> {
+        void::unreachable(self.void)
+    }
+}
+
+impl<Ok> ser::SerializeMap for VoidSerializer<Ok> {
+    type Ok = Ok;
+    type Error = Error;
+
+    fn serialize_key<T: ?Sized + ser::Serialize>(&mut self,
+                                                 _key: &T)
+                                                 -> Result<(), Error> {
+        void::unreachable(self.void)
+    }
+
+    fn serialize_value<T: ?Sized + ser::Serialize>(&mut self,
+                                                   _value: &T)
+                                                   -> Result<(), Error> {
+        void::unreachable(self.void)
+    }
+
+    fn end(self) -> Result<Ok, Error> {
+        void::unreachable(self.void)
+    }
+}
+
+impl<Ok> ser::SerializeStruct for VoidSerializer<Ok> {
+    type Ok = Ok;
+    type Error = Error;
+
+    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
+                                                   _key: &'static str,
+                                                   _value: &T)
+                                                   -> Result<(), Error> {
+        void::unreachable(self.void)
+    }
+
+    fn end(self) -> Result<Ok, Error> {
+        void::unreachable(self.void)
+    }
+}
+
+impl<Ok> ser::SerializeStructVariant for VoidSerializer<Ok> {
+    type Ok = Ok;
+    type Error = Error;
+
+    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
+                                                   _key: &'static str,
+                                                   _value: &T)
+                                                   -> Result<(), Error> {
+        void::unreachable(self.void)
+    }
+
+    fn end(self) -> Result<Ok, Error> {
+        void::unreachable(self.void)
+    }
+}