[Feature] Add the ability for `mold.FieldLevel` to modify the values of other fields.

[ilxqx]

I need a feature that can automatically translate data-dictionary fields in a Struct. Fortunately, I discovered the mold library—its reusability and generality are fascinating, and I’m truly grateful to everyone who has contributed!

However, for my specific requirement it’s still a bit short. I don’t want to touch the field itself that is tagged with trans (although in most cases that’s exactly what people do); instead, I want to modify another field that is strongly associated with it. In my scenario this associated field is, by convention, named “FieldName+Name” (it could also be determined by a tag parameter, but that’s another topic). The main problem right now is that I can’t obtain the reflect.Value of other fields in the struct through mold.FieldLevel.

The code below demonstrates my need, but it doesn’t compile yet:

package main

import (
	"context"
	"fmt"

	"github.com/go-playground/mold/v4"
	"github.com/samber/lo"
)

func main() {
	trans := mold.New()
	trans.SetTagName("trans")
	trans.Register("dict", func(_ context.Context, fl mold.FieldLevel) error {
		if fl.Param() == "user.status" {
			// I can't do this because it would directly overwrite the original value.
			// fl.Field().SetString(
			// 	lo.Ternary(fl.Field().String() == "E", "Enabled", "Disabled"),
			// )

			// I need to save the translated value in another field instead of directly overwriting the original value.
			// This code is just ideal pseudocode; I need something with similar functionality.
			fl.StructField("StatusName").SetString(
				lo.Ternary(fl.Field().String() == "E", "Enabled", "Disabled"),
			)
		}

		return nil
	})

	type Person struct {
		Name       string
		Status     string `trans:"dict=user.status"`
		StatusName string
	}

	person := Person{
		Name:   "John",
		Status: "E",
	}

	if err := trans.Struct(context.Background(), &person); err != nil {
		panic(err)
	}

	fmt.Printf("%#v\n", person)
}

I wonder if it's possible to provide a StructLevel parameter via mold.Func or offer a method through FieldLevel that can access the StructLevel instance it belongs to.