结构字段范围

导出字段

在其他语言中，这类似于公共访问限定符。

• 如果你像我一样来自 ruby，这将使用 attr_accessor 定义属性

如果结构体的字段（即属性）以大写开头，则意味着该字段已导出，因此可以在包外部访问。

假设go项目中有以下文件：

main.go
/library
  /book.go

我们将在它自己的包中定义 book.go。

// library/book.go

// assume we have a package called "library" which contains a book.
package library

// struct that represents a physical book in a library with exported fields
type book struct {
  title string, 
  author string
}

在main.go中使用时：

package main

import (
  "fmt"
  "library" // importing the package that the struct book is in
)

func main() {
  book := library.book{
    title: "book title",
    author: "john snow"
  }
  // print the title and author to show that the struct book fields are accessible outisde it's package "library"
  fmt.println("title:", book.title)
  fmt.println("author:", book.author)
}

在 ruby 中，这与使用 attr_accessor 是同义的，因为我们可以：

• 在类外读写属性值

class book
  # allow read and write on the attributes from outside the class
  attr_accessor(:title, :author)

  def initalize(title = nil, author = nil)
    @title  = title
    @author = authoer
  end
end

# usage outside of the class
book = book.new()

# assinging attributes outside of the class
book.title = "book title"
book.title = "jon snow"

# accessing attributes outside of the class
puts book.title, book.author

私人领域

这类似于其他语言中的私有访问限定符

如果以小写开头，则这些字段将不可访问。

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亲自尝试一下！

假设你的模块名称是 go.mod 中的 myapp

// go.mod
module myapp

go 1.22.5

我们在包library下的library/book.go中创建一个新文件

// library/book.go

// assume we have a package called "library" which contains a book.
package library

// fields start with lowercase, fields are not exported
type book struct {
  title string
  author string
}

将包导入main.go

// main.go
package main

import (
  "fmt"
  // import the library package
  "myapp/library"
)

func main() {
  book := library.book{
    title: "book title",
    author: "john snow"
  }
  // print the title and author to show that the struct book fields are accessible outisde it's package "library"
  fmt.println("title:", book.title)
  fmt.println("author:", book.author)
}

如果您在 vscode 中设置了 go，您会收到以下 lint 错误：

• 标题：“书名

unknown field author in struct literal of type library.Bookcompiler[MissingLitField](https://pkg.go.dev/golang.org/x/tools/internal/typesinternal#MissingLitField