How to unmarshal type alias inside struct from yaml in golang?-Golang-php.cn

How to unmarshal type alias inside struct from yaml in golang?

王林

Release： 2024-02-06 08:57:08

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如何从 golang 中的 yaml 中解组结构内的类型别名？

Question content

I want the following yaml

kind: bar
name: baryaml

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Unmarshalling in structure resource

type kind int

const (
    kind_foo kind = iota
    kind_bar
)

type resource struct {
    kind kind
    name string
}

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Can someone explain why the code below fails to store the correct type, even though it is unmarshalled correctly?

# output:
unmarshaled kind: 1
yamlbar: {0 baryaml}

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# expected output:
unmarshaled kind: 1
yamlbar: {1 baryaml}

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package main

import (
    "fmt"

    "gopkg.in/yaml.v3"
)

type Kind int

const (
    KIND_FOO Kind = iota
    KIND_BAR
)

func (k *Kind) UnmarshalYAML(value *yaml.Node) error {
    var kind string
    err := value.Decode(&kind)

    if err != nil {
        return err
    }

    var x Kind

    switch kind {
    case "foo":
        x = KIND_FOO
    case "bar":
        x = KIND_BAR
    default:
        return fmt.Errorf("unknown kind: %s", kind)
    }

    k = &x
    fmt.Println("Unmarshaled kind:", *k)
    return nil
}

type Resource struct {
    Kind Kind
    Name string
}

func main() {

    var yamlBar = `
kind: bar
name: baryaml
`
    r := Resource{}
    err := yaml.Unmarshal([]byte(yamlBar), &r)

    if err != nil {
        panic(err)
    }

    fmt.Println("yamlBar:", r)
}

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Correct answer

Thanks to @jimb for suggesting dereferencing k Pointer:

func (k *Kind) UnmarshalYAML(value *yaml.Node) error {
    var kind string
    err := value.Decode(&kind)

    if err != nil {
        return err
    }

    switch kind {
    case "foo":
        *k = KIND_FOO
    case "bar":
        *k = KIND_BAR
    default:
        return fmt.Errorf("unknown kind: %s", kind)
    }

    fmt.Println("Unmarshaled kind:", *k)
    return nil
}

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