英文:
anonymous fields in type declaration?
问题
我遇到了这个类型声明：
type Handler func(*Conn)
type Server struct {
Handshake func(*Config, *http.Request) error
Handler
}
（这是https://github.com/golang/net/blob/38c17adf51120973d1735785a7c02f8ce8297c5e/websocket/server.go#L55-L66的简化版本）
Server 结构体中的第二个字段是匿名的。只有类型，没有名称。
这是类型声明的语法（https://golang.org/ref/spec#Type_declarations）：
TypeDecl = "type" ( TypeSpec | "(" { TypeSpec ";" } ")" ) .
TypeSpec = identifier Type .
它明确要求一个标识符名称。但是我引用的那个包含语法的部分也提到了匿名字段。
我不明白为什么这种语法是正确的，以及如何使用匿名字段。
英文:
I came across this type declaration:
type Handler func(*Conn)
type Server struct {
Handshake func(*Config, *http.Request) error
Handler
}
(this is a simplified version of https://github.com/golang/net/blob/38c17adf51120973d1735785a7c02f8ce8297c5e/websocket/server.go#L55-L66
The second field in the Server structure is anonymous. There is just type and no name.
Here is the grammar for type declarations (https://golang.org/ref/spec#Type_declarations):
TypeDecl = "type" ( TypeSpec | "(" { TypeSpec ";" } ")" ) .
TypeSpec = identifier Type .
and it clearly requires an identifier name. But yet the section that I referenced that contains the grammar, also mentions anonymous fields.
I do not understand why this syntax is correct and how anonymous fields are used.
答案1
得分: 2
你想查看与结构有关的语法部分，而不仅仅是类型。请参考：结构类型和AnonymousField的使用。仅查看TypeSpec的产生式会将注意力集中在错误的地方。相反，应该查看FieldDecl；语法表明我们有两种可能性：命名字段（IdentifierList Type）或匿名字段（AnonymousField）。
匿名字段通常用于嵌入。在你的示例中，Server会像Handler一样运行，因为它嵌入了该字段。
英文:
You want to look at the part of the grammar that has to do with structures, not just types. See: Struct types and the use of AnonymousField. Looking just at the production for TypeSpec is focusing attention on the wrong place. Instead, look at FieldDecl; the grammar shows that we have two possibilities: named fields (IdentifierList Type), or anonymous fields (AnonymousField).
Anonymous fields are typically used for embedding. In your example, a Server will act like a Handler because it has embedded that field.
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论