问题

假设我有以下结构体：

type Planet struct {
    Name       string  `json:"name"`
    Aphelion   float64 `json:"aphelion"`   // in million km
    Perihelion float64 `json:"perihelion"` // in million km
    Axis       int64   `json:"axis"`       // in km
    Radius     float64 `json:"radius"`
}

以及该结构体的实例，例如：

var mars = &Planet{
    Name:       "Mars",
    Aphelion:   249.2,
    Perihelion: 206.7,
    Axis:       227939100,
    Radius:     3389.5,
}

var earth = &Planet{
    Name:       "Earth",
    Aphelion:   151.930,
    Perihelion: 147.095,
    Axis:       149598261,
    Radius:     6371.0,
}

var venus = &Planet{
    Name:       "Venus",
    Aphelion:   108.939,
    Perihelion: 107.477,
    Axis:       108208000,
    Radius:     6051.8,
}

现在我想为所有这些实例添加一个字段，例如Mass。我该如何做呢？

目前，我会定义一个新的结构体，例如PlanetWithMass，并逐个字段重新赋值给PlanetWithMass的新实例。

是否有一种更简洁的方法来实现呢？一种不需要在Planet更改时进行调整的方法？

编辑：我需要在 Web 服务器上使用这个结构体，并将其作为 JSON 发送，但需要添加一个额外的字段。嵌入无法解决这个问题，因为它会改变生成的 JSON。

type Planet struct {
    Name       string  `json:"name"`
    Aphelion   float64 `json:"aphelion"`   // in million km
    Perihelion float64 `json:"perihelion"` // in million km
    Axis       int64   `json:"Axis"`       // in km
    Radius     float64 `json:"radius"`
}

var mars = new(Planet)
mars.Name = "Mars"
mars.Aphelion = 249.2
mars.Perihelion = 206.7
mars.Axis = 227939100
mars.Radius = 3389.5

var earth = new(Planet)
earth.Name = "Earth"
earth.Aphelion = 151.930
earth.Perihelion = 147.095
earth.Axis = 149598261
earth.Radius = 6371.0

var venus = new(Planet)
venus.Name = "Venus"
venus.Aphelion = 108.939
venus.Perihelion = 107.477
venus.Axis = 108208000
venus.Radius = 6051.8

答案1

得分: 29

你可以将Planet嵌入到PlanetWithMass中：

type PlanetWithMass struct {
    Planet
    Mass float64
}

然后可以这样使用：

marsWithMass := PlanetWithMass{
    Planet: mars,
    Mass: 639e21,
}

有关嵌入的更多信息，请参阅规范和Effective Go。

➜ Playground

type PlanetWithMass struct {
    Planet
    Mass float64
}

marsWithMass := PlanetWithMass{
    Planet: mars,
    Mass: 639e21,
}

答案2

得分: 1

你可以使用map[string]string，这样可以明确地添加尽可能多的子键。注意：你需要先声明一个具有一种类型的结构体。

type PlanetWithMass struct {
    Planet map[string]string
}

然后，通过结构体的实例来添加更多的字段。

type PlanetWithMass struct {
    Planet map[string]string
}

planet := &PlanetWithMass{} // 结构体的实例

planet.Planet = make(map[string]string) // 将字段声明为map[string]string类型

planet.Planet["Name"] = "Mercury"
planet.Planet["Galaxy"] = "Milky Way"
planet.Planet["Population"] = "70亿"
planet.Planet["HasOceans"] = "是"

使用这种方法，你可以在结构体中添加多个字段，而不必担心使用接口。这可能是一个取巧的方法，但它是有效的！

<details>
<summary>英文:</summary>

You can probably use **map[string]string** which will enable you to explicitly add as many sub keys as possible. NOTE: You will have to declare the struct first with one type

`type PlanetWithMass struct {
	Planet map[string]string
}`

Then to add more fields, start by an instance of the struct


    
   
    type PlanetWithMass struct {
      Planet map[string]string
    }

    planet := &amp;PlanetWithMass{} // instance of struct

	planet.Planet = make(map[string]string) // declare field as a map[string]string

	planet.Planet[&quot;Name&quot;] = &quot;Mercury&quot;
	planet.Planet[&quot;Galaxy&quot;] = &quot;Milky Way&quot;
    planet.Planet[&quot;Population&quot;] = &quot;7 Billion&quot;
	planet.Planet[&quot;HasOceans&quot;] = &quot;Yes&quot;

Using this method, you can add several fields to the struct without the worry of using interfaces. It might be a round hack but it works!



</details>