golang: new 返回值

new 之后会分配内存地址，示例代码：

package main

import (
    "bytes"
    "fmt"
)

func main() {
    var buf *bytes.Buffer
    fmt.Printf("buf init: %p | val: %v\n", buf, buf)

    buf = new(bytes.Buffer) // new 之后会分配内存地址
    fmt.Printf("buf after new: %p | val: %v\n", buf, buf)
    fmt.Printf("new buf is nil: %t\n", buf == nil)

    buf.Write([]byte("done!\n"))
    fmt.Printf("buf after write:%p | val: %v\n", buf, buf)
}

// 运行结果：
/*
MacBook-Pro:new_retVal_aug_15 zhenxink$ go run new_ret_val.go
buf init: 0x0 | val: <nil>
buf after new: 0xc00005e180 | val:
new buf is nil: false
buf after write:0xc00005e180 | val: done!

MacBook-Pro:new_retVal_aug_15 zhenxink$
*/

 

空指针的 bytes.Buffer 不能直接 Write，示例代码：

package main

import (
    "bytes"
    "fmt"
)

func main() {
    var buf *bytes.Buffer
    buf.Write([]byte("done!"))
    fmt.Printf("buf val:%v\n", buf)
}

// 运行结果：
/*
MacBook-Pro:new_retVal_aug_15 zhenxink$ go run nil_buffer_write.go
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x106aec6]

goroutine 1 [running]:
bytes.(*Buffer).Write(0x0, 0xc000068f63, 0x5, 0x5, 0xc000038778, 0xc000068f78, 0x100508f)
    /usr/local/go/src/bytes/buffer.go:169 +0x26
main.main()
    /Users/.../nil_buffer_write.go:10 +0x57
exit status 2
MacBook-Pro:new_retVal_aug_15 zhenxink$
*/ 

// For some types, such as *os.File, nil is a valid receiver, but *bytes.Buffer is not among them.

 

 

 

 

end...