有没有办法将Serde地图转换为价值？(Is there a way to convert a Serde Map into a Value?)
根据Serde规范， Object / Map<String, Value>是一个Value ：
pub enum Value { Null, Bool(bool), Number(Number), String(String), Array(Vec<Value>), Object(Map<String, Value>), }然而，当我编译这段代码时：
extern crate serde; #[macro_use] extern crate serde_json; #[derive(Debug)] struct Wrapper { ok: bool, data: Option<serde_json::Value>, } impl Wrapper { fn ok() -> Wrapper { Wrapper { ok: true, data: None, } } pub fn data(&mut self, data: serde_json::Value) -> &mut Wrapper { self.data = Some(data); self } pub fn finalize(self) -> Wrapper { self } } trait IsValidWrapper { fn is_valid_wrapper(&self) -> bool; } impl IsValidWrapper for serde_json::Map<std::string::String, serde_json::Value> { fn is_valid_wrapper(&self) -> bool { self["ok"].as_bool().unwrap_or(false) } } fn main() { let json = json!({ "name": "John Doe", "age": 43, "phones": [ "+44 1234567", "+44 2345678" ] }); let converted_json: Wrapper = json .as_object() .map_or_else( || Err(json), |obj| { if obj.is_valid_wrapper() { Ok(Wrapper::ok().data(obj["data"].clone()).finalize()) } else { Err(*obj as serde_json::Value) } }, ) .unwrap_or_else(|data| Wrapper::ok().data(data.clone()).finalize()); println!( "org json = {:?} => converted json = {:?}", json, converted_json ); }我收到此错误：
error[E0605]: non-primitive cast: `serde_json::Map<std::string::String, serde_json::Value>` as `serde_json::Value` --> src/main.rs:60:25 | 60 | Err(*obj as serde_json::Value) | ^^^^^^^^^^^^^^^^^^^^^^^^^ | = note: an `as` expression can only be used to convert between primitive types. Consider using the `From` trait有没有办法将Map转换为Value ？
As per the Serde specification, an Object / Map<String, Value> is a Value:
pub enum Value { Null, Bool(bool), Number(Number), String(String), Array(Vec<Value>), Object(Map<String, Value>), }Yet when I compile this code:
extern crate serde; #[macro_use] extern crate serde_json; #[derive(Debug)] struct Wrapper { ok: bool, data: Option<serde_json::Value>, } impl Wrapper { fn ok() -> Wrapper { Wrapper { ok: true, data: None, } } pub fn data(&mut self, data: serde_json::Value) -> &mut Wrapper { self.data = Some(data); self } pub fn finalize(self) -> Wrapper { self } } trait IsValidWrapper { fn is_valid_wrapper(&self) -> bool; } impl IsValidWrapper for serde_json::Map<std::string::String, serde_json::Value> { fn is_valid_wrapper(&self) -> bool { self["ok"].as_bool().unwrap_or(false) } } fn main() { let json = json!({ "name": "John Doe", "age": 43, "phones": [ "+44 1234567", "+44 2345678" ] }); let converted_json: Wrapper = json .as_object() .map_or_else( || Err(json), |obj| { if obj.is_valid_wrapper() { Ok(Wrapper::ok().data(obj["data"].clone()).finalize()) } else { Err(*obj as serde_json::Value) } }, ) .unwrap_or_else(|data| Wrapper::ok().data(data.clone()).finalize()); println!( "org json = {:?} => converted json = {:?}", json, converted_json ); }I get this error:
error[E0605]: non-primitive cast: `serde_json::Map<std::string::String, serde_json::Value>` as `serde_json::Value` --> src/main.rs:60:25 | 60 | Err(*obj as serde_json::Value) | ^^^^^^^^^^^^^^^^^^^^^^^^^ | = note: an `as` expression can only be used to convert between primitive types. Consider using the `From` traitIs there a way to downcast a Map into a Value?
最满意答案
Object / Map<String, Value>是一个Value
不它不是。 Value是一种类型。 Map<String, Value>是一种类型。 Value::Object是一个枚举变体 ，它不是一个单独的类型。 在这种情况下， Value::Object包含另一个Map<String, Value>类型的Map<String, Value> 。 您必须将变量中的值换行以转换类型：
Err(serde_json::Value::Object(obj))这将引导您解决问题：
error[E0308]: mismatched types --> src/main.rs:57:55 | 57 | Err(serde_json::Value::Object(obj)) | ^^^ expected struct `serde_json::Map`, found reference | = note: expected type `serde_json::Map<std::string::String, serde_json::Value>` found type `&serde_json::Map<std::string::String, serde_json::Value>`as_object返回对包含对象（如果存在）的引用，而不是值本身。 您现在需要match它：
let converted_json = match json { serde_json::Value::Object(obj) => {} _ => {} };像这样的东西：
let converted_json = match json { serde_json::Value::Object(obj) => { if obj.is_valid_wrapper() { let mut w = Wrapper::ok(); w.data(obj["data"].clone()); Ok(w.finalize()) } else { Err(serde_json::Value::Object(obj)) } } other => Err(other), };an Object / Map<String, Value> is a Value
No, it is not. Value is a type. Map<String, Value> is a type. Value::Object is an enum variant, which is not a separate type. In this case, Value::Object holds another value of type Map<String, Value>. You have to wrap the value in the variant to convert the type:
Err(serde_json::Value::Object(obj))This will lead you to the problem:
error[E0308]: mismatched types --> src/main.rs:57:55 | 57 | Err(serde_json::Value::Object(obj)) | ^^^ expected struct `serde_json::Map`, found reference | = note: expected type `serde_json::Map<std::string::String, serde_json::Value>` found type `&serde_json::Map<std::string::String, serde_json::Value>`as_object returns a reference to the contained object (if it's present), not the value itself. You will need to match on it for now:
let converted_json = match json { serde_json::Value::Object(obj) => {} _ => {} };Something like this:
let converted_json = match json { serde_json::Value::Object(obj) => { if obj.is_valid_wrapper() { let mut w = Wrapper::ok(); w.data(obj["data"].clone()); Ok(w.finalize()) } else { Err(serde_json::Value::Object(obj)) } } other => Err(other), };
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