How to change struct tags by generics

I need to create struct with generics with dynamic tags

> e.g. We have one struct with generics Phone[T] and simple struct Company

So Phone can belongs to Company and that means our type would be Phone[Company]

type Company struct{}

type Phone[T any] struct{
   number string `json:"phone_number"`
}

Lets create new variable Phone[Company]

phone1 := Phone[Company]{
   number: "+18888888888"
}

Output of serialized phone1 is

{
   "phone_number": "+18888888888"
}

Question

How to set struct Phone[T] type field tags dynamically to receive json like company_phone_number instead of phone_number?

How can i use generic types in golang tags?

e.g.

type Phone[T any] struct{
   number string `json:"${T or replica name of T type e.t.c}_phone_number"`
}

You can do it only if you rebuild your struct on-the-fly with reflect. There is a package for this (I didn't try it) here.

But instead I recommend you to write a custom MarshalJSON method for the struct which handles the cases based on the type of the variable.

package main

import (
	"encoding/json"
	"errors"
	"fmt"
)

type Phone[T any] struct {
	variableType T
	Number       string
}

func (p Phone[T]) MarshalJSON() ([]byte, error) {
	switch any(p.variableType).(type) {
	case Company:
		return json.Marshal(&struct {
			Number string `json:"company_phone_number"`
		}{
			Number: p.Number,
		})
	case Company2:
		return json.Marshal(&struct {
			Number string `json:"company2_phone_number"`
		}{
			Number: p.Number,
		})
	}
	return []byte{}, errors.New("Invalid type")
}

type Company struct {
}

type Company2 struct {
}

func main() {
	p := Phone[Company]{
		Number: "123",
	}

	p2 := Phone[Company2]{
		Number: "321",
	}

	data1, _ := json.Marshal(p)
	data2, _ := json.Marshal(p2)
	fmt.Println(p, string(data1))
	fmt.Println(p2, string(data2))
}

Playground

If you want to avoid the switch you can get the variable type with reflect.TypeOf(p.variableType).Name() but then you have to write a custom JSON marshaler to represent the byte slice with the custom json tags.

It's imposible!

For your case you can redesign your architecture