service/vendor/github.com/xuri/excelize/v2/lib.go

838 lines
24 KiB
Go

// Copyright 2016 - 2023 The excelize Authors. All rights reserved. Use of
// this source code is governed by a BSD-style license that can be found in
// the LICENSE file.
//
// Package excelize providing a set of functions that allow you to write to and
// read from XLAM / XLSM / XLSX / XLTM / XLTX files. Supports reading and
// writing spreadsheet documents generated by Microsoft Excel™ 2007 and later.
// Supports complex components by high compatibility, and provided streaming
// API for generating or reading data from a worksheet with huge amounts of
// data. This library needs Go version 1.16 or later.
package excelize
import (
"archive/zip"
"bytes"
"container/list"
"encoding/xml"
"fmt"
"io"
"math/big"
"os"
"regexp"
"strconv"
"strings"
)
// ReadZipReader extract spreadsheet with given options.
func (f *File) ReadZipReader(r *zip.Reader) (map[string][]byte, int, error) {
var (
err error
docPart = map[string]string{
"[content_types].xml": defaultXMLPathContentTypes,
"xl/sharedstrings.xml": defaultXMLPathSharedStrings,
}
fileList = make(map[string][]byte, len(r.File))
worksheets int
unzipSize int64
)
for _, v := range r.File {
fileSize := v.FileInfo().Size()
unzipSize += fileSize
if unzipSize > f.options.UnzipSizeLimit {
return fileList, worksheets, newUnzipSizeLimitError(f.options.UnzipSizeLimit)
}
fileName := strings.ReplaceAll(v.Name, "\\", "/")
if partName, ok := docPart[strings.ToLower(fileName)]; ok {
fileName = partName
}
if strings.EqualFold(fileName, defaultXMLPathSharedStrings) && fileSize > f.options.UnzipXMLSizeLimit {
if tempFile, err := f.unzipToTemp(v); err == nil {
f.tempFiles.Store(fileName, tempFile)
continue
}
}
if strings.HasPrefix(strings.ToLower(fileName), "xl/worksheets/sheet") {
worksheets++
if fileSize > f.options.UnzipXMLSizeLimit && !v.FileInfo().IsDir() {
if tempFile, err := f.unzipToTemp(v); err == nil {
f.tempFiles.Store(fileName, tempFile)
continue
}
}
}
if fileList[fileName], err = readFile(v); err != nil {
return nil, 0, err
}
}
return fileList, worksheets, nil
}
// unzipToTemp unzip the zip entity to the system temporary directory and
// returned the unzipped file path.
func (f *File) unzipToTemp(zipFile *zip.File) (string, error) {
tmp, err := os.CreateTemp(os.TempDir(), "excelize-")
if err != nil {
return "", err
}
rc, err := zipFile.Open()
if err != nil {
return tmp.Name(), err
}
if _, err = io.Copy(tmp, rc); err != nil {
return tmp.Name(), err
}
if err = rc.Close(); err != nil {
return tmp.Name(), err
}
return tmp.Name(), tmp.Close()
}
// readXML provides a function to read XML content as bytes.
func (f *File) readXML(name string) []byte {
if content, _ := f.Pkg.Load(name); content != nil {
return content.([]byte)
}
if content, ok := f.streams[name]; ok {
return content.rawData.buf.Bytes()
}
return []byte{}
}
// readBytes read file as bytes by given path.
func (f *File) readBytes(name string) []byte {
content := f.readXML(name)
if len(content) != 0 {
return content
}
file, err := f.readTemp(name)
if err != nil {
return content
}
content, _ = io.ReadAll(file)
f.Pkg.Store(name, content)
_ = file.Close()
return content
}
// readTemp read file from system temporary directory by given path.
func (f *File) readTemp(name string) (file *os.File, err error) {
path, ok := f.tempFiles.Load(name)
if !ok {
return
}
file, err = os.Open(path.(string))
return
}
// saveFileList provides a function to update given file content in file list
// of spreadsheet.
func (f *File) saveFileList(name string, content []byte) {
f.Pkg.Store(name, append([]byte(xml.Header), content...))
}
// Read file content as string in an archive file.
func readFile(file *zip.File) ([]byte, error) {
rc, err := file.Open()
if err != nil {
return nil, err
}
dat := make([]byte, 0, file.FileInfo().Size())
buff := bytes.NewBuffer(dat)
_, _ = io.Copy(buff, rc)
return buff.Bytes(), rc.Close()
}
// SplitCellName splits cell name to column name and row number.
//
// Example:
//
// excelize.SplitCellName("AK74") // return "AK", 74, nil
func SplitCellName(cell string) (string, int, error) {
alpha := func(r rune) bool {
return ('A' <= r && r <= 'Z') || ('a' <= r && r <= 'z') || (r == 36)
}
if strings.IndexFunc(cell, alpha) == 0 {
i := strings.LastIndexFunc(cell, alpha)
if i >= 0 && i < len(cell)-1 {
col, rowStr := strings.ReplaceAll(cell[:i+1], "$", ""), cell[i+1:]
if row, err := strconv.Atoi(rowStr); err == nil && row > 0 {
return col, row, nil
}
}
}
return "", -1, newInvalidCellNameError(cell)
}
// JoinCellName joins cell name from column name and row number.
func JoinCellName(col string, row int) (string, error) {
normCol := strings.Map(func(rune rune) rune {
switch {
case 'A' <= rune && rune <= 'Z':
return rune
case 'a' <= rune && rune <= 'z':
return rune - 32
}
return -1
}, col)
if len(col) == 0 || len(col) != len(normCol) {
return "", newInvalidColumnNameError(col)
}
if row < 1 {
return "", newInvalidRowNumberError(row)
}
return normCol + strconv.Itoa(row), nil
}
// ColumnNameToNumber provides a function to convert Excel sheet column name
// (case-insensitive) to int. The function returns an error if column name
// incorrect.
//
// Example:
//
// excelize.ColumnNameToNumber("AK") // returns 37, nil
func ColumnNameToNumber(name string) (int, error) {
if len(name) == 0 {
return -1, newInvalidColumnNameError(name)
}
col := 0
multi := 1
for i := len(name) - 1; i >= 0; i-- {
r := name[i]
if r >= 'A' && r <= 'Z' {
col += int(r-'A'+1) * multi
} else if r >= 'a' && r <= 'z' {
col += int(r-'a'+1) * multi
} else {
return -1, newInvalidColumnNameError(name)
}
multi *= 26
}
if col > MaxColumns {
return -1, ErrColumnNumber
}
return col, nil
}
// ColumnNumberToName provides a function to convert the integer to Excel
// sheet column title.
//
// Example:
//
// excelize.ColumnNumberToName(37) // returns "AK", nil
func ColumnNumberToName(num int) (string, error) {
if num < MinColumns || num > MaxColumns {
return "", ErrColumnNumber
}
var col string
for num > 0 {
col = string(rune((num-1)%26+65)) + col
num = (num - 1) / 26
}
return col, nil
}
// CellNameToCoordinates converts alphanumeric cell name to [X, Y] coordinates
// or returns an error.
//
// Example:
//
// excelize.CellNameToCoordinates("A1") // returns 1, 1, nil
// excelize.CellNameToCoordinates("Z3") // returns 26, 3, nil
func CellNameToCoordinates(cell string) (int, int, error) {
colName, row, err := SplitCellName(cell)
if err != nil {
return -1, -1, newCellNameToCoordinatesError(cell, err)
}
if row > TotalRows {
return -1, -1, ErrMaxRows
}
col, err := ColumnNameToNumber(colName)
return col, row, err
}
// CoordinatesToCellName converts [X, Y] coordinates to alpha-numeric cell
// name or returns an error.
//
// Example:
//
// excelize.CoordinatesToCellName(1, 1) // returns "A1", nil
// excelize.CoordinatesToCellName(1, 1, true) // returns "$A$1", nil
func CoordinatesToCellName(col, row int, abs ...bool) (string, error) {
if col < 1 || row < 1 {
return "", fmt.Errorf("invalid cell reference [%d, %d]", col, row)
}
sign := ""
for _, a := range abs {
if a {
sign = "$"
}
}
colName, err := ColumnNumberToName(col)
return sign + colName + sign + strconv.Itoa(row), err
}
// rangeRefToCoordinates provides a function to convert range reference to a
// pair of coordinates.
func rangeRefToCoordinates(ref string) ([]int, error) {
rng := strings.Split(strings.ReplaceAll(ref, "$", ""), ":")
if len(rng) < 2 {
return nil, ErrParameterInvalid
}
return cellRefsToCoordinates(rng[0], rng[1])
}
// cellRefsToCoordinates provides a function to convert cell range to a
// pair of coordinates.
func cellRefsToCoordinates(firstCell, lastCell string) ([]int, error) {
coordinates := make([]int, 4)
var err error
coordinates[0], coordinates[1], err = CellNameToCoordinates(firstCell)
if err != nil {
return coordinates, err
}
coordinates[2], coordinates[3], err = CellNameToCoordinates(lastCell)
return coordinates, err
}
// sortCoordinates provides a function to correct the cell range, such
// correct C1:B3 to B1:C3.
func sortCoordinates(coordinates []int) error {
if len(coordinates) != 4 {
return ErrCoordinates
}
if coordinates[2] < coordinates[0] {
coordinates[2], coordinates[0] = coordinates[0], coordinates[2]
}
if coordinates[3] < coordinates[1] {
coordinates[3], coordinates[1] = coordinates[1], coordinates[3]
}
return nil
}
// coordinatesToRangeRef provides a function to convert a pair of coordinates
// to range reference.
func (f *File) coordinatesToRangeRef(coordinates []int, abs ...bool) (string, error) {
if len(coordinates) != 4 {
return "", ErrCoordinates
}
firstCell, err := CoordinatesToCellName(coordinates[0], coordinates[1], abs...)
if err != nil {
return "", err
}
lastCell, err := CoordinatesToCellName(coordinates[2], coordinates[3], abs...)
if err != nil {
return "", err
}
return firstCell + ":" + lastCell, err
}
// getDefinedNameRefTo convert defined name to reference range.
func (f *File) getDefinedNameRefTo(definedNameName string, currentSheet string) (refTo string) {
var workbookRefTo, worksheetRefTo string
for _, definedName := range f.GetDefinedName() {
if definedName.Name == definedNameName {
// worksheet scope takes precedence over scope workbook when both definedNames exist
if definedName.Scope == "Workbook" {
workbookRefTo = definedName.RefersTo
}
if definedName.Scope == currentSheet {
worksheetRefTo = definedName.RefersTo
}
}
}
refTo = workbookRefTo
if worksheetRefTo != "" {
refTo = worksheetRefTo
}
return
}
// flatSqref convert reference sequence to cell reference list.
func (f *File) flatSqref(sqref string) (cells map[int][][]int, err error) {
var coordinates []int
cells = make(map[int][][]int)
for _, ref := range strings.Fields(sqref) {
rng := strings.Split(ref, ":")
switch len(rng) {
case 1:
var col, row int
col, row, err = CellNameToCoordinates(rng[0])
if err != nil {
return
}
cells[col] = append(cells[col], []int{col, row})
case 2:
if coordinates, err = rangeRefToCoordinates(ref); err != nil {
return
}
_ = sortCoordinates(coordinates)
for c := coordinates[0]; c <= coordinates[2]; c++ {
for r := coordinates[1]; r <= coordinates[3]; r++ {
cells[c] = append(cells[c], []int{c, r})
}
}
}
}
return
}
// inCoordinates provides a method to check if a coordinate is present in
// coordinates array, and return the index of its location, otherwise
// return -1.
func inCoordinates(a [][]int, x []int) int {
for idx, n := range a {
if x[0] == n[0] && x[1] == n[1] {
return idx
}
}
return -1
}
// inStrSlice provides a method to check if an element is present in an array,
// and return the index of its location, otherwise return -1.
func inStrSlice(a []string, x string, caseSensitive bool) int {
for idx, n := range a {
if !caseSensitive && strings.EqualFold(x, n) {
return idx
}
if x == n {
return idx
}
}
return -1
}
// inFloat64Slice provides a method to check if an element is present in a
// float64 array, and return the index of its location, otherwise return -1.
func inFloat64Slice(a []float64, x float64) int {
for idx, n := range a {
if x == n {
return idx
}
}
return -1
}
// boolPtr returns a pointer to a bool with the given value.
func boolPtr(b bool) *bool { return &b }
// intPtr returns a pointer to an int with the given value.
func intPtr(i int) *int { return &i }
// uintPtr returns a pointer to an int with the given value.
func uintPtr(i uint) *uint { return &i }
// float64Ptr returns a pointer to a float64 with the given value.
func float64Ptr(f float64) *float64 { return &f }
// stringPtr returns a pointer to a string with the given value.
func stringPtr(s string) *string { return &s }
// Value extracts string data type text from a attribute value.
func (attr *attrValString) Value() string {
if attr != nil && attr.Val != nil {
return *attr.Val
}
return ""
}
// Value extracts boolean data type value from a attribute value.
func (attr *attrValBool) Value() bool {
if attr != nil && attr.Val != nil {
return *attr.Val
}
return false
}
// Value extracts float64 data type numeric from a attribute value.
func (attr *attrValFloat) Value() float64 {
if attr != nil && attr.Val != nil {
return *attr.Val
}
return 0
}
// MarshalXML convert the boolean data type to literal values 0 or 1 on
// serialization.
func (avb attrValBool) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
attr := xml.Attr{
Name: xml.Name{
Space: start.Name.Space,
Local: "val",
},
Value: "0",
}
if avb.Val != nil {
if *avb.Val {
attr.Value = "1"
} else {
attr.Value = "0"
}
}
start.Attr = []xml.Attr{attr}
if err := e.EncodeToken(start); err != nil {
return err
}
return e.EncodeToken(start.End())
}
// UnmarshalXML convert the literal values true, false, 1, 0 of the XML
// attribute to boolean data type on deserialization.
func (avb *attrValBool) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
for {
t, err := d.Token()
if err != nil {
return err
}
found := false
switch t.(type) {
case xml.StartElement:
return ErrAttrValBool
case xml.EndElement:
found = true
}
if found {
break
}
}
for _, attr := range start.Attr {
if attr.Name.Local == "val" {
if attr.Value == "" {
val := true
avb.Val = &val
} else {
val, err := strconv.ParseBool(attr.Value)
if err != nil {
return err
}
avb.Val = &val
}
return nil
}
}
defaultVal := true
avb.Val = &defaultVal
return nil
}
// namespaceStrictToTransitional provides a method to convert Strict and
// Transitional namespaces.
func namespaceStrictToTransitional(content []byte) []byte {
namespaceTranslationDic := map[string]string{
StrictNameSpaceDocumentPropertiesVariantTypes: NameSpaceDocumentPropertiesVariantTypes.Value,
StrictNameSpaceDrawingMLMain: NameSpaceDrawingMLMain,
StrictNameSpaceExtendedProperties: NameSpaceExtendedProperties,
StrictNameSpaceSpreadSheet: NameSpaceSpreadSheet.Value,
StrictSourceRelationship: SourceRelationship.Value,
StrictSourceRelationshipChart: SourceRelationshipChart,
StrictSourceRelationshipComments: SourceRelationshipComments,
StrictSourceRelationshipExtendProperties: SourceRelationshipExtendProperties,
StrictSourceRelationshipImage: SourceRelationshipImage,
StrictSourceRelationshipOfficeDocument: SourceRelationshipOfficeDocument,
}
for s, n := range namespaceTranslationDic {
content = bytesReplace(content, []byte(s), []byte(n), -1)
}
return content
}
// bytesReplace replace source bytes with given target.
func bytesReplace(s, source, target []byte, n int) []byte {
if n == 0 {
return s
}
if len(source) < len(target) {
return bytes.Replace(s, source, target, n)
}
if n < 0 {
n = len(s)
}
var wid, i, j, w int
for i, j = 0, 0; i < len(s) && j < n; j++ {
wid = bytes.Index(s[i:], source)
if wid < 0 {
break
}
w += copy(s[w:], s[i:i+wid])
w += copy(s[w:], target)
i += wid + len(source)
}
w += copy(s[w:], s[i:])
return s[:w]
}
// genSheetPasswd provides a method to generate password for worksheet
// protection by given plaintext. When an Excel sheet is being protected with
// a password, a 16-bit (two byte) long hash is generated. To verify a
// password, it is compared to the hash. Obviously, if the input data volume
// is great, numerous passwords will match the same hash. Here is the
// algorithm to create the hash value:
//
// take the ASCII values of all characters shift left the first character 1 bit,
// the second 2 bits and so on (use only the lower 15 bits and rotate all higher bits,
// the highest bit of the 16-bit value is always 0 [signed short])
// XOR all these values
// XOR the count of characters
// XOR the constant 0xCE4B
func genSheetPasswd(plaintext string) string {
var password int64 = 0x0000
var charPos uint = 1
for _, v := range plaintext {
value := int64(v) << charPos
charPos++
rotatedBits := value >> 15 // rotated bits beyond bit 15
value &= 0x7fff // first 15 bits
password ^= value | rotatedBits
}
password ^= int64(len(plaintext))
password ^= 0xCE4B
return strings.ToUpper(strconv.FormatInt(password, 16))
}
// getRootElement extract root element attributes by given XML decoder.
func getRootElement(d *xml.Decoder) []xml.Attr {
tokenIdx := 0
for {
token, _ := d.Token()
if token == nil {
break
}
switch startElement := token.(type) {
case xml.StartElement:
tokenIdx++
if tokenIdx == 1 {
return startElement.Attr
}
}
}
return nil
}
// genXMLNamespace generate serialized XML attributes with a multi namespace
// by given element attributes.
func genXMLNamespace(attr []xml.Attr) string {
var rootElement string
for _, v := range attr {
if lastSpace := getXMLNamespace(v.Name.Space, attr); lastSpace != "" {
if lastSpace == NameSpaceXML {
lastSpace = "xml"
}
rootElement += fmt.Sprintf("%s:%s=\"%s\" ", lastSpace, v.Name.Local, v.Value)
continue
}
rootElement += fmt.Sprintf("%s=\"%s\" ", v.Name.Local, v.Value)
}
return strings.TrimSpace(rootElement) + ">"
}
// getXMLNamespace extract XML namespace from specified element name and attributes.
func getXMLNamespace(space string, attr []xml.Attr) string {
for _, attribute := range attr {
if attribute.Value == space {
return attribute.Name.Local
}
}
return space
}
// replaceNameSpaceBytes provides a function to replace the XML root element
// attribute by the given component part path and XML content.
func (f *File) replaceNameSpaceBytes(path string, contentMarshal []byte) []byte {
sourceXmlns := []byte(`xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main">`)
targetXmlns := []byte(templateNamespaceIDMap)
if attr, ok := f.xmlAttr[path]; ok {
targetXmlns = []byte(genXMLNamespace(attr))
}
return bytesReplace(contentMarshal, sourceXmlns, bytes.ReplaceAll(targetXmlns, []byte(" mc:Ignorable=\"r\""), []byte{}), -1)
}
// addNameSpaces provides a function to add an XML attribute by the given
// component part path.
func (f *File) addNameSpaces(path string, ns xml.Attr) {
exist := false
mc := false
ignore := -1
if attr, ok := f.xmlAttr[path]; ok {
for i, attribute := range attr {
if attribute.Name.Local == ns.Name.Local && attribute.Name.Space == ns.Name.Space {
exist = true
}
if attribute.Name.Local == "Ignorable" && getXMLNamespace(attribute.Name.Space, attr) == "mc" {
ignore = i
}
if attribute.Name.Local == "mc" && attribute.Name.Space == "xmlns" {
mc = true
}
}
}
if !exist {
f.xmlAttr[path] = append(f.xmlAttr[path], ns)
if !mc {
f.xmlAttr[path] = append(f.xmlAttr[path], SourceRelationshipCompatibility)
}
if ignore == -1 {
f.xmlAttr[path] = append(f.xmlAttr[path], xml.Attr{
Name: xml.Name{Local: "Ignorable", Space: "mc"},
Value: ns.Name.Local,
})
return
}
f.setIgnorableNameSpace(path, ignore, ns)
}
}
// setIgnorableNameSpace provides a function to set XML namespace as ignorable
// by the given attribute.
func (f *File) setIgnorableNameSpace(path string, index int, ns xml.Attr) {
ignorableNS := []string{"c14", "cdr14", "a14", "pic14", "x14", "xdr14", "x14ac", "dsp", "mso14", "dgm14", "x15", "x12ac", "x15ac", "xr", "xr2", "xr3", "xr4", "xr5", "xr6", "xr7", "xr8", "xr9", "xr10", "xr11", "xr12", "xr13", "xr14", "xr15", "x15", "x16", "x16r2", "mo", "mx", "mv", "o", "v"}
if inStrSlice(strings.Fields(f.xmlAttr[path][index].Value), ns.Name.Local, true) == -1 && inStrSlice(ignorableNS, ns.Name.Local, true) != -1 {
f.xmlAttr[path][index].Value = strings.TrimSpace(fmt.Sprintf("%s %s", f.xmlAttr[path][index].Value, ns.Name.Local))
}
}
// addSheetNameSpace add XML attribute for worksheet.
func (f *File) addSheetNameSpace(sheet string, ns xml.Attr) {
name, _ := f.getSheetXMLPath(sheet)
f.addNameSpaces(name, ns)
}
// isNumeric determines whether an expression is a valid numeric type and get
// the precision for the numeric.
func isNumeric(s string) (bool, int, float64) {
if strings.Contains(s, "_") {
return false, 0, 0
}
var decimal big.Float
_, ok := decimal.SetString(s)
if !ok {
return false, 0, 0
}
var noScientificNotation string
flt, _ := decimal.Float64()
noScientificNotation = strconv.FormatFloat(flt, 'f', -1, 64)
return true, len(strings.ReplaceAll(noScientificNotation, ".", "")), flt
}
var (
bstrExp = regexp.MustCompile(`_x[a-fA-F\d]{4}_`)
bstrEscapeExp = regexp.MustCompile(`x[a-fA-F\d]{4}_`)
)
// bstrUnmarshal parses the binary basic string, this will trim escaped string
// literal which not permitted in an XML 1.0 document. The basic string
// variant type can store any valid Unicode character. Unicode's characters
// that cannot be directly represented in XML as defined by the XML 1.0
// specification, shall be escaped using the Unicode numerical character
// representation escape character format _xHHHH_, where H represents a
// hexadecimal character in the character's value. For example: The Unicode
// character 8 is not permitted in an XML 1.0 document, so it shall be
// escaped as _x0008_. To store the literal form of an escape sequence, the
// initial underscore shall itself be escaped (i.e. stored as _x005F_). For
// example: The string literal _x0008_ would be stored as _x005F_x0008_.
func bstrUnmarshal(s string) (result string) {
matches, l, cursor := bstrExp.FindAllStringSubmatchIndex(s, -1), len(s), 0
for _, match := range matches {
result += s[cursor:match[0]]
subStr := s[match[0]:match[1]]
if subStr == "_x005F_" {
cursor = match[1]
result += "_"
continue
}
if bstrExp.MatchString(subStr) {
cursor = match[1]
v, _ := strconv.Unquote(`"\u` + s[match[0]+2:match[1]-1] + `"`)
result += v
}
}
if cursor < l {
result += s[cursor:]
}
return result
}
// bstrMarshal encode the escaped string literal which not permitted in an XML
// 1.0 document.
func bstrMarshal(s string) (result string) {
matches, l, cursor := bstrExp.FindAllStringSubmatchIndex(s, -1), len(s), 0
for _, match := range matches {
result += s[cursor:match[0]]
subStr := s[match[0]:match[1]]
if subStr == "_x005F_" {
cursor = match[1]
if match[1]+6 <= l && bstrEscapeExp.MatchString(s[match[1]:match[1]+6]) {
_, err := strconv.Unquote(`"\u` + s[match[1]+1:match[1]+5] + `"`)
if err == nil {
result += subStr + "x005F" + subStr
continue
}
}
result += subStr + "x005F_"
continue
}
if bstrExp.MatchString(subStr) {
cursor = match[1]
if _, err := strconv.Unquote(`"\u` + s[match[0]+2:match[1]-1] + `"`); err == nil {
result += "_x005F" + subStr
continue
}
}
}
if cursor < l {
result += s[cursor:]
}
return result
}
// Stack defined an abstract data type that serves as a collection of elements.
type Stack struct {
list *list.List
}
// NewStack create a new stack.
func NewStack() *Stack {
l := list.New()
return &Stack{l}
}
// Push a value onto the top of the stack.
func (stack *Stack) Push(value interface{}) {
stack.list.PushBack(value)
}
// Pop the top item of the stack and return it.
func (stack *Stack) Pop() interface{} {
e := stack.list.Back()
if e != nil {
stack.list.Remove(e)
return e.Value
}
return nil
}
// Peek view the top item on the stack.
func (stack *Stack) Peek() interface{} {
e := stack.list.Back()
if e != nil {
return e.Value
}
return nil
}
// Len return the number of items in the stack.
func (stack *Stack) Len() int {
return stack.list.Len()
}
// Empty the stack.
func (stack *Stack) Empty() bool {
return stack.list.Len() == 0
}