如何创建值可以是多种类型之一的 Rust HashMap? [英] How do I create a Rust HashMap where the value can be one of multiple types?

问题描述

我想制作一个包含多种类型的 JSON 对象.这是结构:

I want to make a JSON object which includes multiple types. Here's the structure:

{
    "key1": "value",
    "key2": ["val", "val", "val"]
    "key3": { "keyX": 12 }
}

如何制作一个接受所有这些类型的 HashMap?

How can I make a HashMap which accepts all these types?

我正在尝试这个:

let item = HashMap::new();
item.insert("key1", someString); //type is &str
item.insert("key2", someVecOfStrings); //type is Vec<String>
item.insert("key3", someOtherHashMap); //Type is HashMap<&str, u32>

let response = json::encode(&item).unwrap();

我知道哈希映射没有足够的类型信息，但我不确定如何使它工作.我尝试在 item 上设置显式类型，即 HashMap<&str, Encodable> 但这只是另一个错误.这样做的正确方法是什么?

I know that the hash map does not have enough type info, but I'm not sure how I can make it work. I have tried setting an explicit type on item which was HashMap<&str, Encodable> but then it's just another error. What is the correct way to do this?

推荐答案

您应该在 HashMap 中使用枚举类型作为值.该枚举需要为每种可能的类型(布尔、数字、字符串、列表、映射...)提供一个变体，并为每个变体提供一个适当类型的关联值:

You should use an enum type as value in your HashMap. That enum needs to have a variant for each possible type (boolean, number, string, list, map...) and an associated value of appropriate type for each variant:

enum JsonValue<'a> {
    String(&'a str),
    VecOfString(Vec<String>),
    AnotherHashMap(HashMap<&'a str, u32>),
}

幸运的是，已经有 JSON 值类型的实现, serde_json crate 的一部分，它建立在 serde 板条箱.

Fortunately, there already is an implementation of a JSON value type, part of the serde_json crate which is built on the serde crate.

如果您使用 serde_json crate，您的代码将如下所示:

Here is how your code would look if you used the serde_json crate:

extern crate serde_json;

use serde_json::{Value, Map, Number};

fn main() {
    let mut inner_map = Map::new();
    inner_map.insert("x".to_string(), Value::Number(Number::from(10u64)));
    inner_map.insert("y".to_string(), Value::Number(Number::from(20u64)));

    let mut map = Map::new();
    map.insert("key1".to_string(), Value::String("test".to_string()));
    map.insert(
        "key2".to_string(),
        Value::Array(vec![
            Value::String("a".to_string()),
            Value::String("b".to_string()),
        ]),
    );
    map.insert("key3".to_string(), Value::Object(inner_map));

    println!("{}", serde_json::to_string(&map).unwrap());
    // => {"key1":"test","key2":["a","b"],"key3":{"x":10,"y":20}}
}

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