How to Idiomatically Embed a Struct with a Custom `MarshalJSON()` in Go?

Idiomatic Method for Embedding a Struct with a Custom MarshalJSON()

The challenge arises when an embedded struct defines a customized MarshalJSON() method, causing unexpected JSON serialization behavior when attempting to marshal the containing struct.

Background

Consider the following struct definitions:

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

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

Marshaling the Employee struct as expected is straightforward:

p := Person{"Bob"}
e := Employee{&p, "Sales"}
output, _ := json.Marshal(e)
fmt.Printf("%s\n", string(output))

Output:

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

The Problem

However, defining a custom MarshalJSON() method for the embedded struct, as shown below, disrupts the intended serialization:

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

Now, marshaling the Employee produces output with the name field converted to uppercase but misses the jobRole field:

{"name":"BOB"}

Idiomatic Solution

To maintain the desired serialization behavior, avoid defining a MarshalJSON() method on the embedded struct (Person). Instead, create a separate type encapsulating the custom marshalling logic and embed that type:

type Name string

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

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

This approach isolates the marshalling customization to a dedicated type, preventing unexpected side effects when embedding the Person struct elsewhere.

Example: https://play.golang.org/p/u96T4C6PaY

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