请教一个 Go 的语法问题

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package main import ( "io" "net/http" "net/rpc" "net/rpc/jsonrpc" ) type dd interface{} func main() { // rpc.RegisterName("HelloService", new(HelloService)) http.HandleFunc("/jsonrpc", func(w http.ResponseWriter, r *http.Request) { var conn io.ReadWriteCloser = struct { io.Writer io.ReadCloser }{ ReadCloser: r.Body, // 这里为什么不是 io.ReadCloser 这是一个 go 的语法特性,还是根据一个特性引申出的另一个特性? 叫什么? 谢谢 Writer: w, // dd: 3, } rpc.ServeRequest(jsonrpc.NewServerCodec(conn)) }) http.ListenAndServe(":1234", nil) }

问题在上端代码的注释中.提前表示感谢.

9 replies 2020-07-25 11:11:22 +08:00

&nsp; 1

tikazyq

Jul 22, 2020

用匿名 struct 感觉为啥这么别扭

chaleaoch

Jul 22, 2020

@tikazyq 我知道这是匿名, 匿名没问题,不过为什么"io/"不见连.

Reficul

Jul 23, 2020

结构体嵌套了匿名结构 /接口的时候，引用起来就是类型名。

CoolSpring

Jul 23, 2020 via Android

Embedding?
https://golang.org/doc/effective_go.html#embedding

"If we need to refer to an embedded field directly, the type name of the field, ignoring the package qualifier, serves as a field name"

reus

Jul 23, 2020

这类问题，全都在语言规范里写了的

https://golang.org/ref/spec#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.

这里说了字段名是 unqualified type name，也就是不带 io.

heimeil

Jul 23, 2020

定义 struct 只指定类型不指定字段名，默认就会用类型名称作为字段名，不包含包名

package main

import (
"fmt"
"io"
"reflect"
)

func main() {
type T struct {
Foo string

io.ReadCloser
}

s := reflect.ValueOf(&T{}).Elem()

for i := 0; i < s.NumField(); i++ {
fmt.Printf("%d: %s\n", i, s.Type().Field(i).Name)
}
// 0: Foo
// 1: ReadCloser
}

定义 struct 是定义类型，需要明确指定包名，实例化 struct 是指定字段名

byzf

Jul 23, 2020

建议过一遍入门教程.

chaleaoch

Jul 25, 2020

@byzf 谢谢请问那本入门教程, 我看过 GO 语言圣经和 GO 高级编程两本教材书中的例子没有类似的.

chaleaoch

Jul 25, 2020

@byzf 我说错了,这个例子就是 go 高级编程中的例子,但是他没有说明为什么. Go 语言圣经里面没有类似例子.