[英]Why do I get an UnsupportedType error when serializing to TOML with a manually implemented Serialize for an enum with struct variants?
I'm trying to implement Serialize
for an enum that includes struct variants.我正在尝试为包含结构变体的枚举实现
Serialize
。 The serde.rs documentation indicates the following: serde.rs 文档指出以下内容:
enum E {
// Use three-step process:
// 1. serialize_struct_variant
// 2. serialize_field
// 3. end
Color { r: u8, g: u8, b: u8 },
// Use three-step process:
// 1. serialize_tuple_variant
// 2. serialize_field
// 3. end
Point2D(f64, f64),
// Use serialize_newtype_variant.
Inches(u64),
// Use serialize_unit_variant.
Instance,
}
With that in mind, I proceeded to implemention:考虑到这一点,我开始实施:
use serde::ser::{Serialize, SerializeStructVariant, Serializer};
use serde_derive::Deserialize;
#[derive(Deserialize)]
enum Variants {
VariantA,
VariantB { k: u32, p: f64 },
}
impl Serialize for Variants {
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
where
S: Serializer,
{
match *self {
Variants::VariantA => serializer.serialize_unit_variant("Variants", 0, "VariantA"),
Variants::VariantB { ref k, ref p } => {
let mut state =
serializer.serialize_struct_variant("Variants", 1, "VariantB", 2)?;
state.serialize_field("k", k)?;
state.serialize_field("p", p)?;
state.end()
}
}
}
}
fn main() {
let x = Variants::VariantB { k: 5, p: 5.0 };
let toml_str = toml::to_string(&x).unwrap();
println!("{}", toml_str);
}
The code compiles, but when I run it it fails:代码可以编译,但是当我运行它时失败了:
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: UnsupportedType', src/libcore/result.rs:999:5
note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
I figured the issue must be in my use of the API, so I consulted the API documentation for StructVariant
and it looks practically the same as my code.我认为问题一定出在我对 API 的使用上,因此我查阅了
StructVariant
的 API 文档,它看起来与我的代码几乎相同。 I'm sure I'm missing something, but I don't see it based on the docs and output.我确定我遗漏了一些东西,但我没有根据文档和输出看到它。
The TOML format does not support enums with values: TOML 格式不支持带有值的枚举:
use serde::Serialize; // 1.0.99
use toml; // 0.5.3
#[derive(Serialize)]
enum A {
B(i32),
}
fn main() {
match toml::to_string(&A::B(42)) {
Ok(s) => println!("{}", s),
Err(e) => eprintln!("Error: {}", e),
}
}
Error: unsupported Rust type
It's unclear what you'd like your data structure to map to as TOML.目前尚不清楚您希望将数据结构映射为 TOML。 Using JSON works just fine:
使用 JSON 效果很好:
use serde::Serialize; // 1.0.99
use serde_json; // 1.0.40
#[derive(Serialize)]
enum Variants {
VariantA,
VariantB { k: u32, p: f64 },
}
fn main() {
match serde_json::to_string(&Variants::VariantB { k: 42, p: 42.42 }) {
Ok(s) => println!("{}", s),
Err(e) => eprintln!("Error: {}", e),
}
}
{"VariantB":{"k":42,"p":42.42}}
Enabling external tagging for the enum enables Serde to serialize/deserialize it to TOML:为枚举启用外部标记使 Serde 能够将其序列化/反序列化为 TOML:
#[derive(Deserialize)]
#[serde(tag = "type")]
enum Variants {
VariantA,
VariantB { k: u32, p: f64 },
}
toml::to_string(&Variants::VariantB { k: 42, p: 13.37 })
serializes to序列化为
type = VariantB
k = 42
p = 13.37
This works well in Vec
s and HashMap
s, too.这也适用于
Vec
和HashMap
。
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