Idiomatic way to embed struct with custom MarshalJSON() method

Question

Given the following structs:

type Person {
    Name string `json:\"name\"`
}

type Employee {
    Person
    JobRole string `json:\"jobRole\"`
}

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Answer 1

While this produces a different output than what the OP wants, I think it is still useful as a technique to prevent MarshalJSON of embedded structs from breaking the marshaling of structs that contain them.

There is a proposal for encoding/json to recognize an inline option in struct tags. If that ever gets implemented, then I think avoiding embedding structs for cases like in OP's example might be the best bet.

---

Currently, a reasonable workaround was described in a comment on the Go issue tracker and is the basis for this answer. It consists of defining a new type that will have the same memory layout as the original struct being embedded, but none of the methods:

https://play.golang.org/p/BCwcyIqv0F7

package main

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

type Person struct {
    Name string `json:"name"`
}

func (p *Person) MarshalJSON() ([]byte, error) {
    return json.Marshal(struct {
        Name string `json:"name"`
    }{
        Name: strings.ToUpper(p.Name),
    })
}

// person has all the fields of Person, but none of the methods.
// It exists to be embedded in other structs.
type person Person

type EmployeeBroken struct {
    *Person
    JobRole string `json:"jobRole"`
}

type EmployeeGood struct {
    *person
    JobRole string `json:"jobRole"`
}

func main() {
    {
        p := Person{"Bob"}
        e := EmployeeBroken{&p, "Sales"}
        output, _ := json.Marshal(e)
        fmt.Printf("%s\n", string(output))
    }
    {
        p := Person{"Bob"}
        e := EmployeeGood{(*person)(&p), "Sales"}
        output, _ := json.Marshal(e)
        fmt.Printf("%s\n", string(output))
    }
}

Outputs:

{"name":"BOB"}
{"name":"Bob","jobRole":"Sales"}

The OP wants {"name":"BOB","jobRole":"Sales"}. To achieve that, one would need to "inline" the object returned by Person.MarshalJSON into the object produced by Employee.MashalJSON, excluding the fields defined in Person.