bufio: scanner does not work if you pass a structure item as an argument #52420
Description
What version of Go are you using (go version)?
$ go version: go1.17 linux/amd64
Does this issue reproduce with the latest release?
Yes
Example code
I wrote a code example that demonstrates the problem well.
package main
import (
"bufio"
"fmt"
"os"
)
type Example struct {
file *os.File
}
func NewExample() *Example {
f, _ := os.OpenFile("./fakedata.txt", os.O_APPEND|os.O_RDWR|os.O_CREATE, 0644)
// fakedata.txt is a text file that contains three lines:
// string 01
// string 02
// string 03
ex := Example{
file: f,
}
fmt.Printf("example.file 01: %v\n", &ex.file)
scanner := bufio.NewScanner(ex.file)
fmt.Println(scanner.Err())
for scanner.Scan() {
fmt.Printf("scanner.Text 01(): %v\n", scanner.Text())
}
return &ex
}
func (ex *Example) Scan() {
fmt.Printf("example.file 02: %v\n", &ex.file) // same address!
scanner := bufio.NewScanner(ex.file)
fmt.Println(scanner.Err())
for scanner.Scan() {
fmt.Printf("scanner.Text 02(): %v\n", scanner.Text())
}
}
func main() {
example := NewExample()
/*
scanner.Text_01(): string 01
scanner.Text_01(): string 02
scanner.Text_01(): string 03
*/
example.Scan()
// nothing
}Why doesn't the scanner work if you pass it a file as a structure element, given the same address in memory?
Thanks/