How to use a struct field in another struct without referencing it as a key

In the development of PHP, we often encounter the situation of using the fields of another structure in one structure. However, referencing it directly as a key can lead to cluttered and unmaintainable code. So how to use structure fields in another structure? PHP editor Baicao provides you with a concise and clear solution to make your code clearer and easier to read. Let’s take a look below!

Question content

I want to insert a structure field into another structure without having to use the structure name.

I know I can do this:

type person struct {
  name string
}

type user struct {
  person
  email, password string
}

But it will produce this structure:

user := user{person: person{name: ""}, email: "", password: ""}

How can I do something like this:

type person struct {
  name string
}

type user struct {
  name person.name // here
  email, password string
}

Use it like this

user := User{Name: "", Email: "", Password: ""}

is it possible?

Solution

Simply put, it cannot be done using the current language implementation.

When initializing a literal, you need to be explicit (or, in other words: literal![sic]). Since user contains person, the literal user must contain the literal person, as follows:

    u := user{ 
        person: person{
            name: "bob",
        },
        email: "<a href="https://www.php.cn/link/89fee0513b6668e555959f5dc23238e9" class="__cf_email__" data-cfemail="a5c7cac7e5c7cac7d6d5cad18bc6cac8">[email&#160;protected]</a>",
        password: "you're kidding right?",
    } 

However, once you have a variable of type user, you can leverage the anonymous field to set (or get) the anonymous person# via user ## of name:

    u := user{}
    u.name = "bob"
    u.email = "<a href="https://www.php.cn/link/89fee0513b6668e555959f5dc23238e9" class="__cf_email__" data-cfemail="8fede0edcfede0edfcffe0fba1ece0e2">[email&#160;protected]</a>",
    u.password = "you're kidding right?",

Why does go make me do all this work?

Let's imagine that the inner

person could be initialized the way you are looking for:

    u := user{ name: "bob" }

Now let's imagine further that we later modify the

user structure and add its own name field:

    type user struct {
        person
        name string
        email string
        password string
    }

Now you

can obviously initialize the new name field:

    u := user{ name: "bob" }

Note that this is the same code that initialized

user.person.name before, but now it is initializing user.name. not good.

More questions

There are more traps hidden in such code.

First, add the

name field in user already similarly "destroy" the user variable on the name Unqualified reference to :

    u.name = "bob" // used to set user.person.name, now sets user.name

Additionally, using only anonymous

person fields, the user.person.name field is marshaled by default to json as the "name" field:

    {
        "name": "",
        "email": "",
        "password": ""
    }

If the

name field is added, this is the field marshalled as "name", and user.person.name Fields are not grouped at all >.

You might think you could add a

json tag to user.person.name, like

    type user struct {
        person   `json:"personname"`
        name     string
        email    string
        password string
    }

But

now person is marshaled into an object with a name field:

    {
        "PersonName": {
            "Name": ""
        },
        "Name": "",
        "Email": "",
        "Password": ""
    }

This can happen if you try to change the name of a marshaled field for an anonymous person, even though user does not have a name field .

In short: using anonymous structs as a way of "adding fields" within a struct can be problematic and fragile, and should be avoided.

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