英文:
Is Go struct anonymous field public or private?
问题
我们知道，以大写字母开头的字段是公共的，而以小写字母开头的字段是私有的。但是Golang也支持匿名字段。例如：
type myType struct {
string
}
这些字段是为了嵌入而设计的。但是这个字段是公共的还是私有的？
英文:
As we know, fields start with capital letters are public, and those are not are private. But Golang also support anonymous field. For example:
type myType struct {
string
}
These fields are design for Embedding. But is this field public or private?
答案1
得分: 5
根据结构类型的规范：
声明了类型但没有显式字段名的字段被称为嵌入字段。嵌入字段必须被指定为类型名T或非接口类型名*T的指针，并且T本身不能是指针类型。未限定的类型名充当字段名。
string的未限定名称是string。
根据导出标识符的规范：
为了允许从另一个包中访问标识符，可以将其导出。如果满足以下两个条件，则标识符被导出：
- 标识符名称的第一个字符是Unicode大写字母（Unicode字符类别为Lu）；
- 标识符在包块中声明，或者它是字段名或方法名。
string的第一个字符不是Unicode大写字母。
由此可见，嵌入字段未被导出，换句话说，它对包是私有的。
英文:
From the specification on struct types:
> A field declared with a type but no explicit field name is called an embedded field. An embedded field must be specified as a type name T or as a pointer to a non-interface type name *T, and T itself may not be a pointer type. The unqualified type name acts as the field name.
The unqualified name of string is string.
From the specification on exported identifiers:
> An identifier may be exported to permit access to it from another package. An identifier is exported if both:
> 1. the first character of the identifier's name is a Unicode uppercase letter (Unicode character category Lu); and
> 1. the identifier is declared in the package block or it is a field name or method name.
The first character of string is not a Unicode uppercase letter.
It follows that the embedded field is not exported. In other words, it's private to the package.
答案2
得分: 3
如果嵌入类型的类型名称是小写字母开头的，它具有包可见性。例如：
type T struct {
string
}
func main() {
x := T{}
x.string = "a"
fmt.Println(x)
}
然而，如果你将类型 T 移动到另一个包 p 中：
package p
type T struct {
string
}
package main
import "testmod/p"
func main() {
x := p.T{}
x.string = "a" // 错误
}
英文:
If the typename of the embedded type is lower case, it has package visibility. For example:
type T struct {
string
}
func main() {
x := T{}
x.string = "a"
fmt.Println(x)
}
However if you move type T to another package p:
package p
type T struct {
string
}
package main
import "testmod/p"
func main() {
x := p.T{}
x.string = "a" // Error
}
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