go - 如何将类型为其他结构的 map 添加到 map ？

Question

type Email struct { 

    From string
    To string
    Body string

}

type User struct {

    Inbox map[string]Email
    Outbox map[string]Email

}

如何为用户映射/初始化添加值？我非常困惑，如果不是类型Email，我可以添加到用户 map 中，但这非常令人困惑。

Answer 1

map值默认为nil，除非您通过make对其进行初始化。因此，为自己节省一些样板，请为任何具有映射的类型创建一个“构造函数”，以便为您执行此初始化操作，例如

func newUser() User {
    return User{
        Inbox:  make(map[string]Email),
        Outbox: make(map[string]Email),
    }
}

使用方法:

u := newUser()
u.Inbox["gmail#56"] = Email{
    From: "me",
    To:   "you",
    Body: "how are you?",
}
u.Outbox["outlook#25"] = Email{
    From: "Mr. Smith",
    To:   "Bossman",
    Body: "report is done?",
}

游乐场示例:https://play.golang.org/p/3LLurNsDJER

您还可以内联初始化 map ，但是语法非常繁琐:

u := User{
    Inbox:  map[string]Email{"gmail": Email{From: "me", To: "you", Body: "how are you?"}},
    Outbox: map[string]Email{"outlook": Email{From: "Mr. Smith", To: "Bossman", Body: "report is done?"}},
}