interface - 在 Go 中的结构中使用接口(interface)

Question

在试图理解 Go 时，我在 websocket.go 中遇到了这段代码(已截取):

type frameHandler interface {
    HandleFrame(frame frameReader) (r frameReader, err error)
    WriteClose(status int) (err error)
}

// Conn represents a WebSocket connection.
type Conn struct {
    config  *Config
    request *http.Request
    .
    .
    frameHandler
    PayloadType        byte
    defaultCloseStatus int
}

在 Conn 类型中，frameHandler 独自站在那里？没有名字的接口(interface)？后来在代码中，他们甚至尝试检查糟糕的接口(interface)是否为 nil:

Conn(a).frameHandler == nil

我自己的猜测是结构中的 frameHandler 是一个与 frameHandler 接口(interface)匹配的类型，并且在其之上将具有名称 frameHandler。它是否正确？呵呵，无论如何都是有趣的语言。

Answer 1

这一行:

    frameHandler

大致等同于:

    frameHandler frameHandler

在 frameHandler 中，既是字段的名称，也是它的类型。此外，它将frameHandler的所有字段和方法添加到Conn中，所以如果conn是一个Conn，则conn.WriteClose(0)表示conn.frameHandler.WriteClose(0)。

作为the Go Programming Language Specification说:

A field declared with a type but no explicit field name is an anonymous field (colloquially called an embedded field). Such a field type 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.

// A struct with four anonymous fields of type T1, *T2, P.T3 and *P.T4struct {    T1        // field name is T1    *T2       // field name is T2    P.T3      // field name is T3    *P.T4     // field name is T4    x, y int  // field names are x and y}

The following declaration is illegal because field names must be unique in a struct type:

struct {    T         // conflicts with anonymous field *T and *P.T    *T        // conflicts with anonymous field T and *P.T    *P.T      // conflicts with anonymous field T and *T}

Fields and methods (§Method declarations) of an anonymous field are promoted to be ordinary fields and methods of the struct (§Selectors). The following rules apply for a struct type named S and a type named T:

• If S contains an anonymous field T, the method set of S includes the method set of T.
• If S contains an anonymous field *T, the method set of S includes the method set of *T (which itself includes the method set of T).
• If S contains an anonymous field T or *T, the method set of *S includes the method set of *T (which itself includes the method set of T).

A field declaration may be followed by an optional string literal tag, which becomes an attribute for all the fields in the corresponding field declaration. The tags are made visible through a reflection interface but are otherwise ignored.

// A struct corresponding to the TimeStamp protocol buffer.// The tag strings define the protocol buffer field numbers.struct {    microsec  uint64 "field 1"    serverIP6 uint64 "field 2"    process   string "field 3"}