pub trait Visitor<'de>: Sized {
type Value;
Show 28 methods
// Required method
fn expecting(&self, formatter: &mut Formatter<'_>) -> Result;
// Provided methods
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))
}
}
}Required Associated Types§
Required Methods§
sourcefn expecting(&self, formatter: &mut Formatter<'_>) -> Result
fn expecting(&self, formatter: &mut Formatter<'_>) -> Result
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§
sourcefn visit_bool<E>(self, v: bool) -> Result<Self::Value, E>where
E: Error,
fn visit_bool<E>(self, v: bool) -> Result<Self::Value, E>where
E: Error,
The input contains a boolean.
The default implementation fails with a type error.
sourcefn visit_i8<E>(self, v: i8) -> Result<Self::Value, E>where
E: Error,
fn visit_i8<E>(self, v: i8) -> Result<Self::Value, E>where
E: Error,
The input contains an i8.
The default implementation forwards to visit_i64.
sourcefn visit_i16<E>(self, v: i16) -> Result<Self::Value, E>where
E: Error,
fn visit_i16<E>(self, v: i16) -> Result<Self::Value, E>where
E: Error,
The input contains an i16.
The default implementation forwards to visit_i64.
sourcefn visit_i32<E>(self, v: i32) -> Result<Self::Value, E>where
E: Error,
fn visit_i32<E>(self, v: i32) -> Result<Self::Value, E>where
E: Error,
The input contains an i32.
The default implementation forwards to visit_i64.
sourcefn visit_i64<E>(self, v: i64) -> Result<Self::Value, E>where
E: Error,
fn visit_i64<E>(self, v: i64) -> Result<Self::Value, E>where
E: Error,
The input contains an i64.
The default implementation fails with a type error.
sourcefn visit_i128<E>(self, v: i128) -> Result<Self::Value, E>where
E: Error,
fn visit_i128<E>(self, v: i128) -> Result<Self::Value, E>where
E: Error,
The input contains a i128.
The default implementation fails with a type error.
sourcefn visit_u8<E>(self, v: u8) -> Result<Self::Value, E>where
E: Error,
fn visit_u8<E>(self, v: u8) -> Result<Self::Value, E>where
E: Error,
The input contains a u8.
The default implementation forwards to visit_u64.
sourcefn visit_u16<E>(self, v: u16) -> Result<Self::Value, E>where
E: Error,
fn visit_u16<E>(self, v: u16) -> Result<Self::Value, E>where
E: Error,
The input contains a u16.
The default implementation forwards to visit_u64.
sourcefn visit_u32<E>(self, v: u32) -> Result<Self::Value, E>where
E: Error,
fn visit_u32<E>(self, v: u32) -> Result<Self::Value, E>where
E: Error,
The input contains a u32.
The default implementation forwards to visit_u64.
sourcefn visit_u64<E>(self, v: u64) -> Result<Self::Value, E>where
E: Error,
fn visit_u64<E>(self, v: u64) -> Result<Self::Value, E>where
E: Error,
The input contains a u64.
The default implementation fails with a type error.
sourcefn visit_u128<E>(self, v: u128) -> Result<Self::Value, E>where
E: Error,
fn visit_u128<E>(self, v: u128) -> Result<Self::Value, E>where
E: Error,
The input contains a u128.
The default implementation fails with a type error.
sourcefn visit_f32<E>(self, v: f32) -> Result<Self::Value, E>where
E: Error,
fn visit_f32<E>(self, v: f32) -> Result<Self::Value, E>where
E: Error,
The input contains an f32.
The default implementation forwards to visit_f64.
sourcefn visit_f64<E>(self, v: f64) -> Result<Self::Value, E>where
E: Error,
fn visit_f64<E>(self, v: f64) -> Result<Self::Value, E>where
E: Error,
The input contains an f64.
The default implementation fails with a type error.
sourcefn visit_char<E>(self, v: char) -> Result<Self::Value, E>where
E: Error,
fn visit_char<E>(self, v: char) -> Result<Self::Value, E>where
E: Error,
The input contains a char.
The default implementation forwards to visit_str as a one-character
string.
sourcefn visit_str<E>(self, v: &str) -> Result<Self::Value, E>where
E: Error,
fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>where
E: Error,
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.
sourcefn visit_borrowed_str<E>(self, v: &'de str) -> Result<Self::Value, E>where
E: Error,
fn visit_borrowed_str<E>(self, v: &'de str) -> Result<Self::Value, E>where
E: Error,
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.
sourcefn visit_string<E>(self, v: String) -> Result<Self::Value, E>where
E: Error,
fn visit_string<E>(self, v: String) -> Result<Self::Value, E>where
E: Error,
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.
sourcefn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>where
E: Error,
fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>where
E: Error,
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.
sourcefn visit_borrowed_bytes<E>(self, v: &'de [u8]) -> Result<Self::Value, E>where
E: Error,
fn visit_borrowed_bytes<E>(self, v: &'de [u8]) -> Result<Self::Value, E>where
E: Error,
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 Postcard 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.
sourcefn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E>where
E: Error,
fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E>where
E: Error,
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>.
sourcefn 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.
sourcefn 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.
sourcefn 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.
sourcefn 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.
sourcefn visit_seq<A>(self, seq: A) -> Result<Self::Value, A::Error>where
A: SeqAccess<'de>,
fn visit_seq<A>(self, seq: A) -> Result<Self::Value, A::Error>where
A: SeqAccess<'de>,
The input contains a sequence of elements.
The default implementation fails with a type error.
sourcefn visit_map<A>(self, map: A) -> Result<Self::Value, A::Error>where
A: MapAccess<'de>,
fn visit_map<A>(self, map: A) -> Result<Self::Value, A::Error>where
A: MapAccess<'de>,
The input contains a key-value map.
The default implementation fails with a type error.
sourcefn 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.