Bugfix: deep copy issue with function CopySheet(), relate PR qax-os#108.

Author: xuri

Diff for: excelize_test.go

@@ -682,6 +682,10 @@ func TestCopySheet(t *testing.T) {
 	if err != nil {
 		t.Log(err)
 	}
+	xlsx.SetCellValue("Sheet4", "F1", "Hello")
+	if xlsx.GetCellValue("Sheet1", "F1") == "Hello" {
+		t.Error("Invalid value \"Hello\" in Sheet1")
+	}
 	err = xlsx.Save()
 	if err != nil {
 		t.Log(err)

Diff for: lib.go

@@ -3,6 +3,7 @@ package excelize
 import (
 	"archive/zip"
 	"bytes"
+	"encoding/gob"
 	"io"
 	"log"
 	"math"
@@ -104,3 +105,14 @@ func intOnlyMapF(rune rune) rune {
 	}
 	return -1
 }
+
+// deepCopy provides method to creates a deep copy of whatever is passed to it
+// and returns the copy in an interface. The returned value will need to be
+// asserted to the correct type.
+func deepCopy(dst, src interface{}) error {
+	var buf bytes.Buffer
+	if err := gob.NewEncoder(&buf).Encode(src); err != nil {
+		return err
+	}
+	return gob.NewDecoder(bytes.NewBuffer(buf.Bytes())).Decode(dst)
+}

Diff for: sheet.go

@@ -435,7 +435,8 @@ func (f *File) CopySheet(from, to int) error {
 // target worksheet index.
 func (f *File) copySheet(from, to int) {
 	sheet := f.workSheetReader("sheet" + strconv.Itoa(from))
-	worksheet := *sheet
+	worksheet := xlsxWorksheet{}
+	deepCopy(&worksheet, &sheet)
 	path := "xl/worksheets/sheet" + strconv.Itoa(to) + ".xml"
 	if len(worksheet.SheetViews.SheetView) > 0 {
 		worksheet.SheetViews.SheetView[0].TabSelected = false