带条件语句（if）问题的范围

Question

I'm new to Go and I'm struggling with scope (as others).

The code below generates:

./excel.go:24: err declared and not used
./excel.go:25: sheet declared and not used

Why does this happen? I have declared both err and sheet in the parent scope, haven't I?

Excel.go:

package main

import (
    "os"
    "fmt"
    "github.com/tealeg/xlsx"
)

func main() {
    var file *xlsx.File
    var sheet *xlsx.Sheet
    var row *xlsx.Row
    var cell *xlsx.Cell
    var err error

    fileName := "MyXLSXFile.xlsx"

    if _, err := os.Stat(fileName); os.IsNotExist(err) {
        fmt.Printf("File does not exist so create one");
        file = xlsx.NewFile()
        sheet, err = file.AddSheet("Sheet1")
    } else {
        fmt.Printf("File exists so open");
        file, err := xlsx.OpenFile(fileName) // <-- line 24
        sheet := file.Sheets[0] // <-- line 25
    }

    row = sheet.AddRow()

    cell = row.AddCell()
    cell.Value = "I am a cell!"
    cell = row.AddCell()
    cell.Value = "I am another cell!"

    err = file.Save(fileName)

    if err != nil {
        fmt.Printf("help")
    }
}

Answer 1

Use = instead of :=:

    file, err = xlsx.OpenFile(fileName) // <-- line 24
    sheet = file.Sheets[0] // <-- line 25

Go allows re-declaring variables with the same name in nested blocks. := declares a new variable. In your case both err and sheet are declared inside else block but are not used there.