Crate erased_serde
source ·Expand description
This crate provides type-erased versions of Serde’s Serialize
, Serializer
and Deserializer
traits that can be used as trait objects.
The usual Serde Serialize
, Serializer
and Deserializer
traits cannot
be used as trait objects like &dyn Serialize
or boxed trait objects like
Box<dyn Serialize>
because of Rust’s “object safety” rules. In
particular, all three traits contain generic methods which cannot be made
into a trait object.
This library should be considered a low-level building block for interacting
with Serde APIs in an object-safe way. Most use cases will require higher
level functionality such as provided by typetag
which uses this crate
internally.
The traits in this crate work seamlessly with any existing Serde
Serialize
and Deserialize
type and any existing Serde Serializer
and
Deserializer
format.
§Serialization
use erased_serde::{Serialize, Serializer};
use std::collections::BTreeMap as Map;
use std::io;
fn main() {
// Construct some serializers.
let json = &mut serde_json::Serializer::new(io::stdout());
let cbor = &mut serde_cbor::Serializer::new(serde_cbor::ser::IoWrite::new(io::stdout()));
// The values in this map are boxed trait objects. Ordinarily this would not
// be possible with serde::Serializer because of object safety, but type
// erasure makes it possible with erased_serde::Serializer.
let mut formats: Map<&str, Box<dyn Serializer>> = Map::new();
formats.insert("json", Box::new(<dyn Serializer>::erase(json)));
formats.insert("cbor", Box::new(<dyn Serializer>::erase(cbor)));
// These are boxed trait objects as well. Same thing here - type erasure
// makes this possible.
let mut values: Map<&str, Box<dyn Serialize>> = Map::new();
values.insert("vec", Box::new(vec!["a", "b"]));
values.insert("int", Box::new(65536));
// Pick a Serializer out of the formats map.
let format = formats.get_mut("json").unwrap();
// Pick a Serialize out of the values map.
let value = values.get("vec").unwrap();
// This line prints `["a","b"]` to stdout.
value.erased_serialize(format).unwrap();
}
§Deserialization
use erased_serde::Deserializer;
use std::collections::BTreeMap as Map;
fn main() {
static JSON: &'static [u8] = br#"{"A": 65, "B": 66}"#;
static CBOR: &'static [u8] = &[162, 97, 65, 24, 65, 97, 66, 24, 66];
// Construct some deserializers.
let json = &mut serde_json::Deserializer::from_slice(JSON);
let cbor = &mut serde_cbor::Deserializer::from_slice(CBOR);
// The values in this map are boxed trait objects, which is not possible
// with the normal serde::Deserializer because of object safety.
let mut formats: Map<&str, Box<dyn Deserializer>> = Map::new();
formats.insert("json", Box::new(<dyn Deserializer>::erase(json)));
formats.insert("cbor", Box::new(<dyn Deserializer>::erase(cbor)));
// Pick a Deserializer out of the formats map.
let format = formats.get_mut("json").unwrap();
let data: Map<String, usize> = erased_serde::deserialize(format).unwrap();
println!("{}", data["A"] + data["B"]);
}
Macros§
- Implement
serde::Serialize
for a trait object that haserased_serde::Serialize
as a supertrait.
Structs§
- Error when a
Serializer
orDeserializer
trait object fails.
Traits§
- An object-safe equivalent of Serde’s
Deserializer
trait. - An object-safe equivalent of Serde’s
Serialize
trait. - An object-safe equivalent of Serde’s
Serializer
trait.
Functions§
- Deserialize a value of type
T
from the given trait object. - Serialize the given type-erased serializable value.
Type Aliases§
- Result type alias where the error is
erased_serde::Error
.