/libgo/go/strings/strings.go
Go | 559 lines | 405 code | 47 blank | 107 comment | 147 complexity | 09aea55ba9faaadb8b3183d2a77c9567 MD5 | raw file
- // Copyright 2009 The Go Authors. All rights reserved.
- // Use of this source code is governed by a BSD-style
- // license that can be found in the LICENSE file.
- // A package of simple functions to manipulate strings.
- package strings
- import (
- "unicode"
- "utf8"
- )
- // explode splits s into an array of UTF-8 sequences, one per Unicode character (still strings) up to a maximum of n (n < 0 means no limit).
- // Invalid UTF-8 sequences become correct encodings of U+FFF8.
- func explode(s string, n int) []string {
- if n == 0 {
- return nil
- }
- l := utf8.RuneCountInString(s)
- if n <= 0 || n > l {
- n = l
- }
- a := make([]string, n)
- var size, rune int
- i, cur := 0, 0
- for ; i+1 < n; i++ {
- rune, size = utf8.DecodeRuneInString(s[cur:])
- a[i] = string(rune)
- cur += size
- }
- // add the rest, if there is any
- if cur < len(s) {
- a[i] = s[cur:]
- }
- return a
- }
- // Count counts the number of non-overlapping instances of sep in s.
- func Count(s, sep string) int {
- if sep == "" {
- return utf8.RuneCountInString(s) + 1
- }
- c := sep[0]
- l := len(sep)
- n := 0
- if l == 1 {
- // special case worth making fast
- for i := 0; i < len(s); i++ {
- if s[i] == c {
- n++
- }
- }
- return n
- }
- for i := 0; i+l <= len(s); i++ {
- if s[i] == c && s[i:i+l] == sep {
- n++
- i += l - 1
- }
- }
- return n
- }
- // Contains returns true if substr is within s.
- func Contains(s, substr string) bool {
- return Index(s, substr) != -1
- }
- // Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
- func Index(s, sep string) int {
- n := len(sep)
- if n == 0 {
- return 0
- }
- c := sep[0]
- if n == 1 {
- // special case worth making fast
- for i := 0; i < len(s); i++ {
- if s[i] == c {
- return i
- }
- }
- return -1
- }
- // n > 1
- for i := 0; i+n <= len(s); i++ {
- if s[i] == c && s[i:i+n] == sep {
- return i
- }
- }
- return -1
- }
- // LastIndex returns the index of the last instance of sep in s, or -1 if sep is not present in s.
- func LastIndex(s, sep string) int {
- n := len(sep)
- if n == 0 {
- return len(s)
- }
- c := sep[0]
- if n == 1 {
- // special case worth making fast
- for i := len(s) - 1; i >= 0; i-- {
- if s[i] == c {
- return i
- }
- }
- return -1
- }
- // n > 1
- for i := len(s) - n; i >= 0; i-- {
- if s[i] == c && s[i:i+n] == sep {
- return i
- }
- }
- return -1
- }
- // IndexRune returns the index of the first instance of the Unicode code point
- // rune, or -1 if rune is not present in s.
- func IndexRune(s string, rune int) int {
- for i, c := range s {
- if c == rune {
- return i
- }
- }
- return -1
- }
- // IndexAny returns the index of the first instance of any Unicode code point
- // from chars in s, or -1 if no Unicode code point from chars is present in s.
- func IndexAny(s, chars string) int {
- if len(chars) > 0 {
- for i, c := range s {
- for _, m := range chars {
- if c == m {
- return i
- }
- }
- }
- }
- return -1
- }
- // LastIndexAny returns the index of the last instance of any Unicode code
- // point from chars in s, or -1 if no Unicode code point from chars is
- // present in s.
- func LastIndexAny(s, chars string) int {
- if len(chars) > 0 {
- for i := len(s); i > 0; {
- rune, size := utf8.DecodeLastRuneInString(s[0:i])
- i -= size
- for _, m := range chars {
- if rune == m {
- return i
- }
- }
- }
- }
- return -1
- }
- // Generic split: splits after each instance of sep,
- // including sepSave bytes of sep in the subarrays.
- func genSplit(s, sep string, sepSave, n int) []string {
- if n == 0 {
- return nil
- }
- if sep == "" {
- return explode(s, n)
- }
- if n < 0 {
- n = Count(s, sep) + 1
- }
- c := sep[0]
- start := 0
- a := make([]string, n)
- na := 0
- for i := 0; i+len(sep) <= len(s) && na+1 < n; i++ {
- if s[i] == c && (len(sep) == 1 || s[i:i+len(sep)] == sep) {
- a[na] = s[start : i+sepSave]
- na++
- start = i + len(sep)
- i += len(sep) - 1
- }
- }
- a[na] = s[start:]
- return a[0 : na+1]
- }
- // Split slices s into substrings separated by sep and returns a slice of
- // the substrings between those separators.
- // If sep is empty, Split splits after each UTF-8 sequence.
- // The count determines the number of substrings to return:
- // n > 0: at most n substrings; the last substring will be the unsplit remainder.
- // n == 0: the result is nil (zero substrings)
- // n < 0: all substrings
- func Split(s, sep string, n int) []string { return genSplit(s, sep, 0, n) }
- // SplitAfter slices s into substrings after each instance of sep and
- // returns a slice of those substrings.
- // If sep is empty, Split splits after each UTF-8 sequence.
- // The count determines the number of substrings to return:
- // n > 0: at most n substrings; the last substring will be the unsplit remainder.
- // n == 0: the result is nil (zero substrings)
- // n < 0: all substrings
- func SplitAfter(s, sep string, n int) []string {
- return genSplit(s, sep, len(sep), n)
- }
- // Fields splits the string s around each instance of one or more consecutive white space
- // characters, returning an array of substrings of s or an empty list if s contains only white space.
- func Fields(s string) []string {
- return FieldsFunc(s, unicode.IsSpace)
- }
- // FieldsFunc splits the string s at each run of Unicode code points c satisfying f(c)
- // and returns an array of slices of s. If all code points in s satisfy f(c) or the
- // string is empty, an empty slice is returned.
- func FieldsFunc(s string, f func(int) bool) []string {
- // First count the fields.
- n := 0
- inField := false
- for _, rune := range s {
- wasInField := inField
- inField = !f(rune)
- if inField && !wasInField {
- n++
- }
- }
- // Now create them.
- a := make([]string, n)
- na := 0
- fieldStart := -1 // Set to -1 when looking for start of field.
- for i, rune := range s {
- if f(rune) {
- if fieldStart >= 0 {
- a[na] = s[fieldStart:i]
- na++
- fieldStart = -1
- }
- } else if fieldStart == -1 {
- fieldStart = i
- }
- }
- if fieldStart != -1 { // Last field might end at EOF.
- a[na] = s[fieldStart:]
- }
- return a
- }
- // Join concatenates the elements of a to create a single string. The separator string
- // sep is placed between elements in the resulting string.
- func Join(a []string, sep string) string {
- if len(a) == 0 {
- return ""
- }
- if len(a) == 1 {
- return a[0]
- }
- n := len(sep) * (len(a) - 1)
- for i := 0; i < len(a); i++ {
- n += len(a[i])
- }
- b := make([]byte, n)
- bp := 0
- for i := 0; i < len(a); i++ {
- s := a[i]
- for j := 0; j < len(s); j++ {
- b[bp] = s[j]
- bp++
- }
- if i+1 < len(a) {
- s = sep
- for j := 0; j < len(s); j++ {
- b[bp] = s[j]
- bp++
- }
- }
- }
- return string(b)
- }
- // HasPrefix tests whether the string s begins with prefix.
- func HasPrefix(s, prefix string) bool {
- return len(s) >= len(prefix) && s[0:len(prefix)] == prefix
- }
- // HasSuffix tests whether the string s ends with suffix.
- func HasSuffix(s, suffix string) bool {
- return len(s) >= len(suffix) && s[len(s)-len(suffix):] == suffix
- }
- // Map returns a copy of the string s with all its characters modified
- // according to the mapping function. If mapping returns a negative value, the character is
- // dropped from the string with no replacement.
- func Map(mapping func(rune int) int, s string) string {
- // In the worst case, the string can grow when mapped, making
- // things unpleasant. But it's so rare we barge in assuming it's
- // fine. It could also shrink but that falls out naturally.
- maxbytes := len(s) // length of b
- nbytes := 0 // number of bytes encoded in b
- b := make([]byte, maxbytes)
- for _, c := range s {
- rune := mapping(c)
- if rune >= 0 {
- wid := 1
- if rune >= utf8.RuneSelf {
- wid = utf8.RuneLen(rune)
- }
- if nbytes+wid > maxbytes {
- // Grow the buffer.
- maxbytes = maxbytes*2 + utf8.UTFMax
- nb := make([]byte, maxbytes)
- copy(nb, b[0:nbytes])
- b = nb
- }
- nbytes += utf8.EncodeRune(b[nbytes:maxbytes], rune)
- }
- }
- return string(b[0:nbytes])
- }
- // Repeat returns a new string consisting of count copies of the string s.
- func Repeat(s string, count int) string {
- b := make([]byte, len(s)*count)
- bp := 0
- for i := 0; i < count; i++ {
- for j := 0; j < len(s); j++ {
- b[bp] = s[j]
- bp++
- }
- }
- return string(b)
- }
- // ToUpper returns a copy of the string s with all Unicode letters mapped to their upper case.
- func ToUpper(s string) string { return Map(unicode.ToUpper, s) }
- // ToLower returns a copy of the string s with all Unicode letters mapped to their lower case.
- func ToLower(s string) string { return Map(unicode.ToLower, s) }
- // ToTitle returns a copy of the string s with all Unicode letters mapped to their title case.
- func ToTitle(s string) string { return Map(unicode.ToTitle, s) }
- // ToUpperSpecial returns a copy of the string s with all Unicode letters mapped to their
- // upper case, giving priority to the special casing rules.
- func ToUpperSpecial(_case unicode.SpecialCase, s string) string {
- return Map(func(r int) int { return _case.ToUpper(r) }, s)
- }
- // ToLowerSpecial returns a copy of the string s with all Unicode letters mapped to their
- // lower case, giving priority to the special casing rules.
- func ToLowerSpecial(_case unicode.SpecialCase, s string) string {
- return Map(func(r int) int { return _case.ToLower(r) }, s)
- }
- // ToTitleSpecial returns a copy of the string s with all Unicode letters mapped to their
- // title case, giving priority to the special casing rules.
- func ToTitleSpecial(_case unicode.SpecialCase, s string) string {
- return Map(func(r int) int { return _case.ToTitle(r) }, s)
- }
- // isSeparator reports whether the rune could mark a word boundary.
- // TODO: update when package unicode captures more of the properties.
- func isSeparator(rune int) bool {
- // ASCII alphanumerics and underscore are not separators
- if rune <= 0x7F {
- switch {
- case '0' <= rune && rune <= '9':
- return false
- case 'a' <= rune && rune <= 'z':
- return false
- case 'A' <= rune && rune <= 'Z':
- return false
- case rune == '_':
- return false
- }
- return true
- }
- // Letters and digits are not separators
- if unicode.IsLetter(rune) || unicode.IsDigit(rune) {
- return false
- }
- // Otherwise, all we can do for now is treat spaces as separators.
- return unicode.IsSpace(rune)
- }
- // BUG(r): The rule Title uses for word boundaries does not handle Unicode punctuation properly.
- // Title returns a copy of the string s with all Unicode letters that begin words
- // mapped to their title case.
- func Title(s string) string {
- // Use a closure here to remember state.
- // Hackish but effective. Depends on Map scanning in order and calling
- // the closure once per rune.
- prev := ' '
- return Map(
- func(r int) int {
- if isSeparator(prev) {
- prev = r
- return unicode.ToTitle(r)
- }
- prev = r
- return r
- },
- s)
- }
- // TrimLeftFunc returns a slice of the string s with all leading
- // Unicode code points c satisfying f(c) removed.
- func TrimLeftFunc(s string, f func(r int) bool) string {
- i := indexFunc(s, f, false)
- if i == -1 {
- return ""
- }
- return s[i:]
- }
- // TrimRightFunc returns a slice of the string s with all trailing
- // Unicode code points c satisfying f(c) removed.
- func TrimRightFunc(s string, f func(r int) bool) string {
- i := lastIndexFunc(s, f, false)
- if i >= 0 && s[i] >= utf8.RuneSelf {
- _, wid := utf8.DecodeRuneInString(s[i:])
- i += wid
- } else {
- i++
- }
- return s[0:i]
- }
- // TrimFunc returns a slice of the string s with all leading
- // and trailing Unicode code points c satisfying f(c) removed.
- func TrimFunc(s string, f func(r int) bool) string {
- return TrimRightFunc(TrimLeftFunc(s, f), f)
- }
- // IndexFunc returns the index into s of the first Unicode
- // code point satisfying f(c), or -1 if none do.
- func IndexFunc(s string, f func(r int) bool) int {
- return indexFunc(s, f, true)
- }
- // LastIndexFunc returns the index into s of the last
- // Unicode code point satisfying f(c), or -1 if none do.
- func LastIndexFunc(s string, f func(r int) bool) int {
- return lastIndexFunc(s, f, true)
- }
- // indexFunc is the same as IndexFunc except that if
- // truth==false, the sense of the predicate function is
- // inverted.
- func indexFunc(s string, f func(r int) bool, truth bool) int {
- start := 0
- for start < len(s) {
- wid := 1
- rune := int(s[start])
- if rune >= utf8.RuneSelf {
- rune, wid = utf8.DecodeRuneInString(s[start:])
- }
- if f(rune) == truth {
- return start
- }
- start += wid
- }
- return -1
- }
- // lastIndexFunc is the same as LastIndexFunc except that if
- // truth==false, the sense of the predicate function is
- // inverted.
- func lastIndexFunc(s string, f func(r int) bool, truth bool) int {
- for i := len(s); i > 0; {
- rune, size := utf8.DecodeLastRuneInString(s[0:i])
- i -= size
- if f(rune) == truth {
- return i
- }
- }
- return -1
- }
- func makeCutsetFunc(cutset string) func(rune int) bool {
- return func(rune int) bool { return IndexRune(cutset, rune) != -1 }
- }
- // Trim returns a slice of the string s with all leading and
- // trailing Unicode code points contained in cutset removed.
- func Trim(s string, cutset string) string {
- if s == "" || cutset == "" {
- return s
- }
- return TrimFunc(s, makeCutsetFunc(cutset))
- }
- // TrimLeft returns a slice of the string s with all leading
- // Unicode code points contained in cutset removed.
- func TrimLeft(s string, cutset string) string {
- if s == "" || cutset == "" {
- return s
- }
- return TrimLeftFunc(s, makeCutsetFunc(cutset))
- }
- // TrimRight returns a slice of the string s, with all trailing
- // Unicode code points contained in cutset removed.
- func TrimRight(s string, cutset string) string {
- if s == "" || cutset == "" {
- return s
- }
- return TrimRightFunc(s, makeCutsetFunc(cutset))
- }
- // TrimSpace returns a slice of the string s, with all leading
- // and trailing white space removed, as defined by Unicode.
- func TrimSpace(s string) string {
- return TrimFunc(s, unicode.IsSpace)
- }
- // Replace returns a copy of the string s with the first n
- // non-overlapping instances of old replaced by new.
- // If n < 0, there is no limit on the number of replacements.
- func Replace(s, old, new string, n int) string {
- if old == new || n == 0 {
- return s // avoid allocation
- }
- // Compute number of replacements.
- if m := Count(s, old); m == 0 {
- return s // avoid allocation
- } else if n < 0 || m < n {
- n = m
- }
- // Apply replacements to buffer.
- t := make([]byte, len(s)+n*(len(new)-len(old)))
- w := 0
- start := 0
- for i := 0; i < n; i++ {
- j := start
- if len(old) == 0 {
- if i > 0 {
- _, wid := utf8.DecodeRuneInString(s[start:])
- j += wid
- }
- } else {
- j += Index(s[start:], old)
- }
- w += copy(t[w:], s[start:j])
- w += copy(t[w:], new)
- start = j + len(old)
- }
- w += copy(t[w:], s[start:])
- return string(t[0:w])
- }