Go语言中接口断言的有效性与io.WriteString的优化策略

func WriteString(w Writer, s string) (n int, err error) {
    if sw, ok := w.(stringWriter); ok {
        return sw.WriteString(s)
    }
    return w.Write([]byte(s))
}

type stringWriter interface {
    WriteString(s string) (n int, err error)
}

type Writer interface {
    Write(p []byte) (n int, err error)
}

package main

import (
    "fmt"
    "io"
)

// 定义一个自定义的stringWriter接口，与io包中的概念类似
type stringWriter interface {
    WriteString(s string) (n int, err error)
}

// LogWriter 是一个具体的类型，用于演示多接口实现
type LogWriter struct {
    totalBytes int
}

// Write 方法实现了 io.Writer 接口
func (lw *LogWriter) Write(p []byte) (n int, err error) {
    fmt.Printf("LogWriter: Writing %d bytes via Write: %s\n", len(p), string(p))
    lw.totalBytes += len(p)
    return len(p), nil
}

// WriteString 方法实现了 stringWriter 接口
func (lw *LogWriter) WriteString(s string) (n int, err error) {
    fmt.Printf("LogWriter: Writing %d characters via WriteString: %s\n", len(s), s)
    // 实际应用中，这里可能会有更高效的字符串处理逻辑
    lw.totalBytes += len(s)
    return len(s), nil
}

func main() {
    myLogWriter := &LogWriter{}

    // 将myLogWriter赋值给io.Writer接口变量
    var writer io.Writer = myLogWriter

    // 调用io.WriteString函数
    // 此时，writer的动态类型是*LogWriter，它同时实现了io.Writer和stringWriter
    // 因此，类型断言 w.(stringWriter) 会成功
    n, err := io.WriteString(writer, "Hello, Go interfaces!")
    if err != nil {
        fmt.Println("Error:", err)
    }
    fmt.Printf("Written %d bytes. Total bytes logged: %d\n", n, myLogWriter.totalBytes)

    fmt.Println("\n--- Testing with a type that only implements io.Writer ---")
    // 假设我们有一个只实现了io.Writer的类型
    type SimpleWriter struct{}
    func (sw SimpleWriter) Write(p []byte) (n int, err error) {
        fmt.Printf("SimpleWriter: Writing %d bytes via Write: %s\n", len(p), string(p))
        return len(p), nil
    }
    var simpleWriter io.Writer = SimpleWriter{}
    n2, err2 := io.WriteString(simpleWriter, "Only SimpleWriter here.")
    if err2 != nil {
        fmt.Println("Error:", err2)
    }
    fmt.Printf("Written %d bytes.\n", n2)
}