如何更新任意go struct的所有字符串字段？

Question

我尝试编写一个函数来更新 arbitrary 结构的所有字符串字段，如下所示：

type Student struct {
  Name  string
  Age   int
}

func SetStringField(obj interface{}) {
    reflect.ValueOf(obj).Elem().FieldByName("Name").SetString("set name")
}

func main() {
  student := Student{
    "alice",
    12,
  }

  SetStringField(&student)
}

但是这个函数只能更新特定的字段。我试试这个：


func SetStringField2(obj interface{}) {
    // Keys := reflect.TypeOf(obj)
    Values := reflect.ValueOf(obj)
    count := reflect.ValueOf(obj).NumField()
    for i := 0; i < count; i++ {
        // fieldKey := Keys.Field(i).Name
        fieldValue := Values.Field(i)
        switch fieldValue.Kind() {
        case reflect.String:
            // fieldValue.CanSet()==false
            fieldValue.SetString("fieldCleanString2 set name")
            // panic: reflect: call of reflect.Value.FieldByName on interface Value
            // reflect.ValueOf(&obj).Elem().FieldByName(fieldKey).SetString("123")
        }
    }
}

func main() {
  student := Student{
    "alice",
    12,
  }
  SetStringField2(student)
}

fieldValue.SetString() 得到 "panic: reflect: reflect.flag.mustBeAssignable using unaddressable value" 因为 fieldValue.CanSet()==false.
reflect.ValueOf(&obj).Elem().FieldByName(fieldKey).SetString("fieldCleanString2 set name") 也失败，得到 "panic: reflect: call of reflect.Value.FieldByName on interface Value".

调用 SetStringField2(&student) 得到 "panic: reflect: call of reflect.Value.NumField on ptr Value"

那么，还有其他方法可以完成这项工作吗？

Answer 1

解决方案 1：

package service

import (
    "fmt"
    "reflect"
    "testing"
)


func SetStringField2(obj interface{}) {
    Values := reflect.ValueOf(obj).Elem()
    count := reflect.Indirect(reflect.ValueOf(obj)).NumField()
    for i := 0; i < count; i++ {
        fieldValue := Values.Field(i)
        switch fieldValue.Kind() {
        case reflect.String:
            fieldValue.SetString("fieldCleanString2 set name")
        }
    }
}

func TestSetValue(t *testing.T) {

    type Student struct {
        Name string
        Age  int
    }
    student := &Student{
        "alice",
        12,
    }

    SetStringField2(student)

    fmt.Print(student.Name)
}

Answer 2

问题是反射值不可设置。要解决此问题，请从指针创建反射值。

// SetStringField2 sets strings fields on the struct pointed to by ps.
func SetStringField2(ps interface{}) {
    v := reflect.ValueOf(ps).Elem() // Elem() dereferences pointer
    for i := 0; i < v.NumField(); i++ {
        fv := v.Field(i)
        switch fv.Kind() {
        case reflect.String:
            fv.SetString("fieldCleanString2 set name")
        }
    }
}

将指向值的指针传递给函数：

student := Student{
    "alice",
    12,
}
SetStringField2(&student)

Run it on the playground.

如何更新任意go struct的所有字符串字段？

How to update all string fields of arbitrary go struct?

go

reflect