golang：解组动态 YAML 注释

下面是最新的有效演示:

package main

import (
    "fmt"
    "reflect"
    "unsafe"

    "gopkg.in/yaml.v3"
)

type User struct {
    Name string `yaml:"dummy"`
}

func (u *User) UnmarshalYAML(node *yaml.Node) error {
    t := reflect.TypeOf(*u)
    fields := make([]reflect.StructField, 0)

    for i := 0; i < t.NumField(); i++ {
        fields = append(fields, t.Field(i))

        if t.Field(i).Name == "Name" {
            fields[i].Tag = `yaml:"name"` // Dynamic annotation
        }
    }

    newType := reflect.StructOf(fields)
    newValue := reflect.NewAt(newType, unsafe.Pointer(u)).Elem()

    err := node.Decode(newValue.Addr().Interface())
    return err
}

var dat string = `name: abc`

func main() {
    out := User{}
    yaml.Unmarshal([]byte(dat), &out)
    fmt.Printf("%+v\n", out)
}

两个关键变化:

1. 将newValue.Interface()改为newValue.Addr().Interface().(请参阅本例:https://pkg.go.dev/reflect#example-StructOf)

2. 将newValue := value.Convert(newType)替换为newValue := reflect.NewAt(newType, unsafe.Pointer(u)).Elem().

   我们这样做是因为value := reflect.ValueOf(*u)中的value无法寻址(您可以使用fmt.Printf("%v", value.Addr())进行验证.它会panic ，并显示消息panic: reflect.Value.Addr of unaddressable value).