dsifjgogw48491752 2018-12-01 09:49
浏览 502

从Golang中的JSON解析字符串以枚举

I have an enum defined as

type MyEnum int

const(
   FirstEnum MyEnum = iota
)

Then, I have a json that has the key-value pair "Key": "FirstEnum". I'm unmarshalling like this.

var data map[string]interface{}
err := json.Unmarshal([]byte(json), &data)
x := data["key"].(MyEnum)

When I run this, however, I get the error:

panic: interface conversion: interface {} is string, not ps.Protocol [recovered]
        panic: interface conversion: interface {} is string, not ps.Protocol

Is there a way to get this to work like a normal conversion of a string representation of a enum to enum type in Go?

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  • dtyz76562 2018-12-01 10:16
    关注

    I figured out something that works in a similar way (at least works for my current situation):

    Use string for enum-like constants:

    type MyEnum string
    
    const(
       FirstEnum MyEnum = "FirstEnum"
    )
    

    Now, use the decoding json to custom types as mentioned here.

    data := MyJsonStruct{}
    err := json.Unmarshal([]byte(json), &data)
    

    MyJsonStruct would look something like:

    type MyJsonStruct struct {
        Key MyEnum
    }
    

    You can then make MyJsonStruct implement the Unmarshaler interface, so you can validate the given values.

    func (s *MyJsonStruct) UnmarshalJSON(data []byte) error {
        // Define a secondary type so that we don't end up with a recursive call to json.Unmarshal
        type Aux MyJsonStruct;
        var a *Aux = (*Aux)(s);
        err := json.Unmarshal(data, &a)
        if err != nil {
            return err
        }
    
        // Validate the valid enum values
        switch s.Key {
        case FirstEnum, SecondEnum:
            return nil
        default:
            s.Key = ""
            return errors.New("invalid value for Key")
        }
    }
    

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