pub trait Visitor<'de>: Sized {
type Value;
Show 28 methods
fn expecting(&self, formatter: &mut Formatter<'_>) -> Result;
fn visit_bool<E>(self, v: bool) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_i8<E>(self, v: i8) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_i16<E>(self, v: i16) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_i32<E>(self, v: i32) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_i64<E>(self, v: i64) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_i128<E>(self, v: i128) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_u8<E>(self, v: u8) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_u16<E>(self, v: u16) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_u32<E>(self, v: u32) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_u64<E>(self, v: u64) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_u128<E>(self, v: u128) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_f32<E>(self, v: f32) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_f64<E>(self, v: f64) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_char<E>(self, v: char) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_borrowed_str<E>(self, v: &'de str) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_borrowed_bytes<E>(self, v: &'de [u8]) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_none<E>(self) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
where
D: Deserializer<'de>,
{ ... }
fn visit_unit<E>(self) -> Result<Self::Value, E>
where
E: Error,
{ ... }
fn visit_newtype_struct<D>(
self,
deserializer: D
) -> Result<Self::Value, D::Error>
where
D: Deserializer<'de>,
{ ... }
fn visit_seq<A>(self, seq: A) -> Result<Self::Value, A::Error>
where
A: SeqAccess<'de>,
{ ... }
fn visit_map<A>(self, map: A) -> Result<Self::Value, A::Error>
where
A: MapAccess<'de>,
{ ... }
fn visit_enum<A>(self, data: A) -> Result<Self::Value, A::Error>
where
A: EnumAccess<'de>,
{ ... }
}
Expand description
This trait represents a visitor that walks through a deserializer.
Lifetime
The 'de
lifetime of this trait is the requirement for lifetime of data
that may be borrowed by Self::Value
. See the page Understanding
deserializer lifetimes for a more detailed explanation of these lifetimes.
Example
/// A visitor that deserializes a long string - a string containing at least
/// some minimum number of bytes.
struct LongString {
min: usize,
}
impl<'de> Visitor<'de> for LongString {
type Value = String;
fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
write!(formatter, "a string containing at least {} bytes", self.min)
}
fn visit_str<E>(self, s: &str) -> Result<Self::Value, E>
where
E: de::Error,
{
if s.len() >= self.min {
Ok(s.to_owned())
} else {
Err(de::Error::invalid_value(Unexpected::Str(s), &self))
}
}
}
Associated Types
Required methods
Format a message stating what data this Visitor expects to receive.
This is used in error messages. The message should complete the sentence “This Visitor expects to receive …”, for example the message could be “an integer between 0 and 64”. The message should not be capitalized and should not end with a period.
fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
write!(formatter, "an integer between 0 and {}", self.max)
}
Provided methods
The input contains a boolean.
The default implementation fails with a type error.
The input contains an i8
.
The default implementation forwards to visit_i64
.
The input contains an i16
.
The default implementation forwards to visit_i64
.
The input contains an i32
.
The default implementation forwards to visit_i64
.
The input contains an i64
.
The default implementation fails with a type error.
The input contains a i128
.
This method is available only on Rust compiler versions >=1.26. The default implementation fails with a type error.
The input contains a u8
.
The default implementation forwards to visit_u64
.
The input contains a u16
.
The default implementation forwards to visit_u64
.
The input contains a u32
.
The default implementation forwards to visit_u64
.
The input contains a u64
.
The default implementation fails with a type error.
The input contains a u128
.
This method is available only on Rust compiler versions >=1.26. The default implementation fails with a type error.
The input contains an f32
.
The default implementation forwards to visit_f64
.
The input contains an f64
.
The default implementation fails with a type error.
The input contains a char
.
The default implementation forwards to visit_str
as a one-character
string.
The input contains a string. The lifetime of the string is ephemeral and it may be destroyed after this method returns.
This method allows the Deserializer
to avoid a copy by retaining
ownership of any buffered data. Deserialize
implementations that do
not benefit from taking ownership of String
data should indicate that
to the deserializer by using Deserializer::deserialize_str
rather than
Deserializer::deserialize_string
.
It is never correct to implement visit_string
without implementing
visit_str
. Implement neither, both, or just visit_str
.
The input contains a string that lives at least as long as the
Deserializer
.
This enables zero-copy deserialization of strings in some formats. For
example JSON input containing the JSON string "borrowed"
can be
deserialized with zero copying into a &'a str
as long as the input
data outlives 'a
.
The default implementation forwards to visit_str
.
The input contains a string and ownership of the string is being given
to the Visitor
.
This method allows the Visitor
to avoid a copy by taking ownership of
a string created by the Deserializer
. Deserialize
implementations
that benefit from taking ownership of String
data should indicate that
to the deserializer by using Deserializer::deserialize_string
rather
than Deserializer::deserialize_str
, although not every deserializer
will honor such a request.
It is never correct to implement visit_string
without implementing
visit_str
. Implement neither, both, or just visit_str
.
The default implementation forwards to visit_str
and then drops the
String
.
The input contains a byte array. The lifetime of the byte array is ephemeral and it may be destroyed after this method returns.
This method allows the Deserializer
to avoid a copy by retaining
ownership of any buffered data. Deserialize
implementations that do
not benefit from taking ownership of Vec<u8>
data should indicate that
to the deserializer by using Deserializer::deserialize_bytes
rather
than Deserializer::deserialize_byte_buf
.
It is never correct to implement visit_byte_buf
without implementing
visit_bytes
. Implement neither, both, or just visit_bytes
.
The input contains a byte array that lives at least as long as the
Deserializer
.
This enables zero-copy deserialization of bytes in some formats. For
example Bincode data containing bytes can be deserialized with zero
copying into a &'a [u8]
as long as the input data outlives 'a
.
The default implementation forwards to visit_bytes
.
The input contains a byte array and ownership of the byte array is being
given to the Visitor
.
This method allows the Visitor
to avoid a copy by taking ownership of
a byte buffer created by the Deserializer
. Deserialize
implementations that benefit from taking ownership of Vec<u8>
data
should indicate that to the deserializer by using
Deserializer::deserialize_byte_buf
rather than
Deserializer::deserialize_bytes
, although not every deserializer will
honor such a request.
It is never correct to implement visit_byte_buf
without implementing
visit_bytes
. Implement neither, both, or just visit_bytes
.
The default implementation forwards to visit_bytes
and then drops the
Vec<u8>
.
fn visit_none<E>(self) -> Result<Self::Value, E> where
E: Error,
fn visit_none<E>(self) -> Result<Self::Value, E> where
E: Error,
The input contains an optional that is absent.
The default implementation fails with a type error.
fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error> where
D: Deserializer<'de>,
fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error> where
D: Deserializer<'de>,
The input contains an optional that is present.
The default implementation fails with a type error.
fn visit_unit<E>(self) -> Result<Self::Value, E> where
E: Error,
fn visit_unit<E>(self) -> Result<Self::Value, E> where
E: Error,
The input contains a unit ()
.
The default implementation fails with a type error.
fn visit_newtype_struct<D>(
self,
deserializer: D
) -> Result<Self::Value, D::Error> where
D: Deserializer<'de>,
fn visit_newtype_struct<D>(
self,
deserializer: D
) -> Result<Self::Value, D::Error> where
D: Deserializer<'de>,
The input contains a newtype struct.
The content of the newtype struct may be read from the given
Deserializer
.
The default implementation fails with a type error.
The input contains a sequence of elements.
The default implementation fails with a type error.
The input contains a key-value map.
The default implementation fails with a type error.
fn visit_enum<A>(self, data: A) -> Result<Self::Value, A::Error> where
A: EnumAccess<'de>,
fn visit_enum<A>(self, data: A) -> Result<Self::Value, A::Error> where
A: EnumAccess<'de>,
The input contains an enum.
The default implementation fails with a type error.