Augment builtin std/core Deserialize impls to implement deserialize_from

serde/src/de/impls.rs

@@ -15,6 +15,7 @@ use de::{Deserialize, Deserializer, EnumAccess, Error, SeqAccess, Unexpected, Va
 use de::MapAccess;
 
 use de::from_primitive::FromPrimitive;
+use private::de::DeserializeFromSeed;
 
 #[cfg(any(feature = "std", feature = "alloc"))]
 use private::de::size_hint;
@@ -51,6 +52,7 @@ impl<'de> Deserialize<'de> for () {
 
 struct BoolVisitor;
 
+
 impl<'de> Visitor<'de> for BoolVisitor {
     type Value = bool;
 
@@ -210,6 +212,8 @@ impl<'de> Deserialize<'de> for char {
 
 #[cfg(any(feature = "std", feature = "alloc"))]
 struct StringVisitor;
+#[cfg(any(feature = "std", feature = "alloc"))]
+struct StringFromVisitor<'a>(&'a mut String);
 
 #[cfg(any(feature = "std", feature = "alloc"))]
 impl<'de> Visitor<'de> for StringVisitor {
@@ -254,6 +258,59 @@ impl<'de> Visitor<'de> for StringVisitor {
     }
 }
 
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<'a, 'de> Visitor<'de> for StringFromVisitor<'a> {
+    type Value = ();
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("a string")
+    }
+
+    fn visit_str<E>(self, v: &str) -> Result<(), E>
+    where
+        E: Error,
+    {
+        self.0.clear();
+        self.0.push_str(v);
+        Ok(())
+    }
+
+    fn visit_string<E>(self, v: String) -> Result<(), E>
+    where
+        E: Error,
+    {
+        *self.0 = v;
+        Ok(())
+    }
+
+    fn visit_bytes<E>(self, v: &[u8]) -> Result<(), E>
+    where
+        E: Error,
+    {
+        match str::from_utf8(v) {
+            Ok(s) => {
+                self.0.clear();
+                self.0.push_str(s);
+                Ok(())
+            }
+            Err(_) => Err(Error::invalid_value(Unexpected::Bytes(v), &self)),
+        }
+    }
+
+    fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<(), E>
+    where
+        E: Error,
+    {
+        match String::from_utf8(v) {
+            Ok(s) => {
+                *self.0 = s;
+                Ok(())
+            }
+            Err(e) => Err(Error::invalid_value(Unexpected::Bytes(&e.into_bytes()), &self),),
+        }
+    }
+}
+
 #[cfg(any(feature = "std", feature = "alloc"))]
 impl<'de> Deserialize<'de> for String {
     fn deserialize<D>(deserializer: D) -> Result<String, D::Error>
@@ -262,6 +319,13 @@ impl<'de> Deserialize<'de> for String {
     {
         deserializer.deserialize_string(StringVisitor)
     }
+
+    fn deserialize_from<D>(&mut self, deserializer: D) -> Result<(), D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_string(StringFromVisitor(self))
+    }
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -421,6 +485,7 @@ forwarded_impl!((), Box<CStr>, CString::into_boxed_c_str);
 struct OptionVisitor<T> {
     marker: PhantomData<T>,
 }
+struct OptionFromVisitor<'a, T: 'a>(&'a mut Option<T>);
 
 impl<'de, T> Visitor<'de> for OptionVisitor<T>
 where
@@ -457,6 +522,49 @@ where
     }
 }
 
+impl<'a, 'de, T> Visitor<'de> for OptionFromVisitor<'a, T>
+where
+    T: Deserialize<'de>,
+{
+    type Value = ();
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("option")
+    }
+
+    #[inline]
+    fn visit_unit<E>(self) -> Result<(), E>
+    where
+        E: Error,
+    {
+        *self.0 = None;
+        Ok(())
+    }
+
+    #[inline]
+    fn visit_none<E>(self) -> Result<(), E>
+    where
+        E: Error,
+    {
+        *self.0 = None;
+        Ok(())
+    }
+
+    #[inline]
+    fn visit_some<D>(self, deserializer: D) -> Result<(), D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        // The some enum's repr is opaque, so we can't play cute tricks with
+        // its tag to build this in place unconditionally.
+        //
+        // FIXME: investigate whether branching on the old value being Some to
+        // deserialize_from the value is profitable (probably data-dependent?)
+        *self.0 = try!(T::deserialize(deserializer).map(Some));
+        Ok(())
+    }
+}
+
 impl<'de, T> Deserialize<'de> for Option<T>
 where
     T: Deserialize<'de>,
@@ -467,6 +575,13 @@ where
     {
         deserializer.deserialize_option(OptionVisitor { marker: PhantomData })
     }
+
+    fn deserialize_from<D>(&mut self, deserializer: D) -> Result<(), D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_option(OptionFromVisitor(self))
+    }
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -509,7 +624,9 @@ macro_rules! seq_impl {
         $ty:ident < T $(: $tbound1:ident $(+ $tbound2:ident)*)* $(, $typaram:ident : $bound1:ident $(+ $bound2:ident)*)* >,
         $access:ident,
         $ctor:expr,
+        $clear:expr,
         $with_capacity:expr,
+        $reserve:expr,
         $insert:expr
     ) => {
         impl<'de, T $(, $typaram)*> Deserialize<'de> for $ty<T $(, $typaram)*>
@@ -554,16 +671,59 @@ macro_rules! seq_impl {
                 let visitor = SeqVisitor { marker: PhantomData };
                 deserializer.deserialize_seq(visitor)
             }
+
+            fn deserialize_from<D>(&mut self, deserializer: D) -> Result<(), D::Error>
+            where
+                D: Deserializer<'de>,
+            {
+                struct SeqVisitor<'a, T: 'a $(, $typaram: 'a)*>(&'a mut $ty<T $(, $typaram)*>);
+
+                impl<'a, 'de, T $(, $typaram)*> Visitor<'de> for SeqVisitor<'a, T $(, $typaram)*>
+                where
+                    T: Deserialize<'de> $(+ $tbound1 $(+ $tbound2)*)*,
+                    $($typaram: $bound1 $(+ $bound2)*,)*
+                {
+                    type Value = ();
+
+                    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                        formatter.write_str("a sequence")
+                    }
+
+                    #[inline]
+                    fn visit_seq<A>(mut self, mut $access: A) -> Result<(), A::Error>
+                    where
+                        A: SeqAccess<'de>,
+                    {
+                        $clear(&mut self.0);
+                        $reserve(&mut self.0, size_hint::cautious($access.size_hint()));
+
+                        // FIXME: try to overwrite old values here? (Vec, VecDeque, LinkedList)
+                        while let Some(value) = try!($access.next_element()) {
+                            $insert(&mut self.0, value);
+                        }
+
+                        Ok(())
+                    }
+                }
+
+                deserializer.deserialize_seq(SeqVisitor(self))
+            }
         }
     }
 }
 
+// Dummy impl of reserve
+#[cfg(any(feature = "std", feature = "alloc"))]
+fn nop_reserve<T, U>(_x: T, _y: U) { }
+
 #[cfg(any(feature = "std", feature = "alloc"))]
 seq_impl!(
     BinaryHeap<T: Ord>,
     seq,
     BinaryHeap::new(),
+    BinaryHeap::clear,
     BinaryHeap::with_capacity(size_hint::cautious(seq.size_hint())),
+    BinaryHeap::reserve,
     BinaryHeap::push);
 
 #[cfg(any(feature = "std", feature = "alloc"))]
@@ -571,7 +731,9 @@ seq_impl!(
     BTreeSet<T: Eq + Ord>,
     seq,
     BTreeSet::new(),
+    BTreeSet::clear,
     BTreeSet::new(),
+    nop_reserve,
     BTreeSet::insert);
 
 #[cfg(any(feature = "std", feature = "alloc"))]
@@ -579,7 +741,9 @@ seq_impl!(
     LinkedList<T>,
     seq,
     LinkedList::new(),
+    LinkedList::clear,
     LinkedList::new(),
+    nop_reserve,
     LinkedList::push_back);
 
 #[cfg(feature = "std")]
@@ -587,7 +751,9 @@ seq_impl!(
     HashSet<T: Eq + Hash, S: BuildHasher + Default>,
     seq,
     HashSet::with_hasher(S::default()),
+    HashSet::clear,
     HashSet::with_capacity_and_hasher(size_hint::cautious(seq.size_hint()), S::default()),
+    HashSet::reserve,
     HashSet::insert);
 
 #[cfg(any(feature = "std", feature = "alloc"))]
@@ -595,7 +761,9 @@ seq_impl!(
     Vec<T>,
     seq,
     Vec::new(),
+    Vec::clear,
     Vec::with_capacity(size_hint::cautious(seq.size_hint())),
+    Vec::reserve,
     Vec::push);
 
 #[cfg(any(feature = "std", feature = "alloc"))]
@@ -603,7 +771,9 @@ seq_impl!(
     VecDeque<T>,
     seq,
     VecDeque::new(),
+    VecDeque::clear,
     VecDeque::with_capacity(size_hint::cautious(seq.size_hint())),
+    VecDeque::reserve,
     VecDeque::push_back);
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -611,6 +781,7 @@ seq_impl!(
 struct ArrayVisitor<A> {
     marker: PhantomData<A>,
 }
+struct ArrayFromVisitor<'a, A: 'a>(&'a mut A);
 
 impl<A> ArrayVisitor<A> {
     fn new() -> Self {
@@ -673,6 +844,35 @@ macro_rules! array_impls {
                 }
             }
 
+            impl<'a, 'de, T> Visitor<'de> for ArrayFromVisitor<'a, [T; $len]>
+            where
+                T: Deserialize<'de>,
+            {
+                type Value = ();
+
+                fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                    formatter.write_str(concat!("an array of length ", $len))
+                }
+
+                #[inline]
+                fn visit_seq<A>(self, mut seq: A) -> Result<(), A::Error>
+                where
+                    A: SeqAccess<'de>,
+                {
+                    let mut fail_idx = None;
+                    for (idx, dest) in self.0[..].iter_mut().enumerate() {
+                        if try!(seq.next_element_seed(DeserializeFromSeed(dest))).is_none() {
+                            fail_idx = Some(idx);
+                            break;
+                        }
+                    }
+                    if let Some(idx) = fail_idx {
+                        return Err(Error::invalid_length(idx, &self));
+                    }
+                    Ok(())
+                }
+            }
+
             impl<'de, T> Deserialize<'de> for [T; $len]
             where
                 T: Deserialize<'de>,
@@ -683,6 +883,13 @@ macro_rules! array_impls {
                 {
                     deserializer.deserialize_tuple($len, ArrayVisitor::<[T; $len]>::new())
                 }
+
+                fn deserialize_from<D>(&mut self, deserializer: D) -> Result<(), D::Error>
+                where
+                    D: Deserializer<'de>,
+                {
+                    deserializer.deserialize_tuple($len, ArrayFromVisitor(self))
+                }
             }
         )+
     }
@@ -726,49 +933,76 @@ array_impls! {
 ////////////////////////////////////////////////////////////////////////////////
 
 macro_rules! tuple_impls {
-    ($($len:tt $visitor:ident => ($($n:tt $name:ident)+))+) => {
+    ($($len:tt => ($($n:tt $name:ident)+))+) => {
         $(
-            struct $visitor<$($name,)+> {
-                marker: PhantomData<($($name,)+)>,
-            }
-
-            impl<$($name,)+> $visitor<$($name,)+> {
-                fn new() -> Self {
-                    $visitor { marker: PhantomData }
-                }
-            }
-
-            impl<'de, $($name: Deserialize<'de>),+> Visitor<'de> for $visitor<$($name,)+> {
-                type Value = ($($name,)+);
-
-                fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
-                    formatter.write_str(concat!("a tuple of size ", $len))
-                }
-
-                #[inline]
-                #[allow(non_snake_case)]
-                fn visit_seq<A>(self, mut seq: A) -> Result<($($name,)+), A::Error>
-                where
-                    A: SeqAccess<'de>,
-                {
-                    $(
-                        let $name = match try!(seq.next_element()) {
-                            Some(value) => value,
-                            None => return Err(Error::invalid_length($n, &self)),
-                        };
-                    )+
-
-                    Ok(($($name,)+))
-                }
-            }
-
             impl<'de, $($name: Deserialize<'de>),+> Deserialize<'de> for ($($name,)+) {
                 #[inline]
                 fn deserialize<D>(deserializer: D) -> Result<($($name,)+), D::Error>
                 where
                     D: Deserializer<'de>,
                 {
-                    deserializer.deserialize_tuple($len, $visitor::new())
+                    struct TupleVisitor<$($name,)+> {
+                        marker: PhantomData<($($name,)+)>,
+                    }
+
+                    impl<'de, $($name: Deserialize<'de>),+> Visitor<'de> for TupleVisitor<$($name,)+> {
+                        type Value = ($($name,)+);
+
+                        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                            formatter.write_str(concat!("a tuple of size ", $len))
+                        }
+
+                        #[inline]
+                        #[allow(non_snake_case)]
+                        fn visit_seq<A>(self, mut seq: A) -> Result<($($name,)+), A::Error>
+                        where
+                            A: SeqAccess<'de>,
+                        {
+                            $(
+                                let $name = match try!(seq.next_element()) {
+                                    Some(value) => value,
+                                    None => return Err(Error::invalid_length($n, &self)),
+                                };
+                            )+
+
+                            Ok(($($name,)+))
+                        }
+                    }
+
+                    deserializer.deserialize_tuple($len, TupleVisitor { marker: PhantomData })
+                }
+
+                #[inline]
+                fn deserialize_from<D>(&mut self, deserializer: D) -> Result<(), D::Error>
+                where
+                    D: Deserializer<'de>,
+                {
+                    struct TupleVisitor<'a, $($name: 'a,)+>(&'a mut ($($name,)+));
+
+                    impl<'a, 'de, $($name: Deserialize<'de>),+> Visitor<'de> for TupleVisitor<'a, $($name,)+> {
+                        type Value = ();
+
+                        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                            formatter.write_str(concat!("a tuple of size ", $len))
+                        }
+
+                        #[inline]
+                        #[allow(non_snake_case)]
+                        fn visit_seq<A>(self, mut seq:                                                                      A) -> Result<(), A::Error>
+                        where
+                            A: SeqAccess<'de>,
+                        {
+                            $(
+                                if try!(seq.next_element_seed(DeserializeFromSeed(&mut (self.0).$n))).is_none() {
+                                    return Err(Error::invalid_length($n, &self));
+                                }
+                            )+
+
+                            Ok(())
+                        }
+                    }
+
+                    deserializer.deserialize_tuple($len, TupleVisitor(self))
                 }
             }
         )+
@@ -776,22 +1010,22 @@ macro_rules! tuple_impls {
 }
 
 tuple_impls! {
-    1 TupleVisitor1 => (0 T0)
+    1  => (0 T0)
-    2 TupleVisitor2 => (0 T0 1 T1)
+    2  => (0 T0 1 T1)
-    3 TupleVisitor3 => (0 T0 1 T1 2 T2)
+    3  => (0 T0 1 T1 2 T2)
-    4 TupleVisitor4 => (0 T0 1 T1 2 T2 3 T3)
+    4  => (0 T0 1 T1 2 T2 3 T3)
-    5 TupleVisitor5 => (0 T0 1 T1 2 T2 3 T3 4 T4)
+    5  => (0 T0 1 T1 2 T2 3 T3 4 T4)
-    6 TupleVisitor6 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5)
+    6  => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5)
-    7 TupleVisitor7 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6)
+    7  => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6)
-    8 TupleVisitor8 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7)
+    8  => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7)
-    9 TupleVisitor9 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8)
+    9  => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8)
-    10 TupleVisitor10 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9)
+    10 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9)
-    11 TupleVisitor11 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10)
+    11 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10)
-    12 TupleVisitor12 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11)
+    12 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11)
-    13 TupleVisitor13 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11 12 T12)
+    13 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11 12 T12)
-    14 TupleVisitor14 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11 12 T12 13 T13)
+    14 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11 12 T12 13 T13)
-    15 TupleVisitor15 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11 12 T12 13 T13 14 T14)
+    15 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11 12 T12 13 T13 14 T14)
-    16 TupleVisitor16 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11 12 T12 13 T13 14 T14 15 T15)
+    16 => (0 T0 1 T1 2 T2 3 T3 4 T4 5 T5 6 T6 7 T7 8 T8 9 T9 10 T10 11 T11 12 T12 13 T13 14 T14 15 T15)
 }
 
 ////////////////////////////////////////////////////////////////////////////////

serde/src/private/de.rs

@@ -8,7 +8,7 @@
 
 use lib::*;
 
-use de::{Deserialize, Deserializer, IntoDeserializer, Error, Visitor};
+use de::{Deserialize, Deserializer, DeserializeSeed, IntoDeserializer, Error, Visitor};
 
 #[cfg(any(feature = "std", feature = "alloc"))]
 use de::Unexpected;
@@ -2009,3 +2009,20 @@ where
         map struct enum identifier ignored_any
     }
 }
+
+/// A DeserializeSeed helper for implementing deserialize_from Visitors.
+///
+/// Wraps a mutable reference and calls deserialize_from on it.
+pub struct DeserializeFromSeed<'a, T: 'a>(pub &'a mut T);
+
+impl<'a, 'de, T> DeserializeSeed<'de> for DeserializeFromSeed<'a, T>
+    where T: Deserialize<'de>,
+{
+    type Value = ();
+    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+       self.0.deserialize_from(deserializer)
+    }
+}