提升Go的字段和方法

原文

结构是一个包含很多字段名字和类型的集合。通常它是这样的：

package main
import "fmt"
type Person struct {
    name string
    age int32
}
func main() {
    person := Person{name: "Michał", age: 29}
    fmt.Println(person)  // {Michał 29}
}

(在本文章的其余部分，包名，导入，和主函数都会省略掉，不写咯)
上面的结构的每一个字段都有各自的名字。Go也允许跳过字段名字。字段没有名字叫做匿名或者嵌入。类型的名字（没有当前包的前缀）会被当作字段的名字。由于结构的字段名称必须唯一，所以我们不能这样做：

import (
    "net/http"
)
type Request struct{}
type T struct {
    http.Request // field name is "Request"
    Request // field name is "Request"
}

这样编译器会抛出错误：

> go install github.com/mlowicki/sandbox
# github.com/mlowicki/sandbox
src/github.com/mlowicki/sandbox/sandbox.go:34: duplicate field Request

结构内匿名字段的方法和字段可以很简单的访问到：

type Person struct {
    name string
    age int32
}
func (p Person) IsAdult() bool {
    return p.age >= 18
}
type Employee struct {
    position string
}
func (e Employee) IsManager() bool {
    return e.position == "manager"
}
type Record struct {
    Person
    Employee
}
...
record := Record{}
record.name = "Michał"
record.age = 29
record.position = "software engineer"
fmt.Println(record) // {{Michał 29} {software engineer}}
fmt.Println(record.name) // Michał
fmt.Println(record.age) // 29
fmt.Println(record.position) // software engineer
fmt.Println(record.IsAdult()) // true
fmt.Println(record.IsManager()) // false

匿名（嵌入）字段的方法和字段叫做提升。它们看上去像普通字段，但是它们不能通过结构初始化：

//record := Record{}
record := Record{name: "Michał", age: 29}

编译器会抛出错误：

> go install github.com/mlowicki/sandbox
# github.com/mlowicki/sandbox
src/github.com/mlowicki/sandbox/sandbox.go:34: duplicate field Request

如果要声明的话，就必须创建整个匿名（嵌入）字段结构：

Record{Person{name: "Michał", age: 29}, Employee{position: "Software Engineer"}}