golang strings 代码
文件路径：/src/strings/strings.go
/ 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.
/ Package strings implements simple functions to manipulate UTF-8 encoded strings.
/
/ For information about UTF-8 strings in Go, see https://blog.golang.org/strings.
package strings
import (
"internal/bytealg"
"unicode"
"unicode/utf8"
)
/ explode splits s into a slice of UTF-8 strings,
/ one string per Unicode character up to a maximum of n (n < 0 means no limit).
/ Invalid UTF-8 sequences become correct encodings of U+FFFD.
func explode(s string, n int) []string {
l := utf8.RuneCountInString(s)
if n < 0 || n > l {
n = l
}
a := make([]string, n)
for i := 0; i < n-1; i++ {
ch, size := utf8.DecodeRuneInString(s)
a[i] = s[:size]
s = s[size:]
if ch == utf8.RuneError {
a[i] = string(utf8.RuneError)
}
}
if n > 0 {
a[n-1] = s
}
return a
}
/ Count counts the number of non-overlapping instances of substr in s.
/ If substr is an empty string, Count returns 1 + the number of Unicode code points in s.
func Count(s, substr string) int {
/ special case
if len(substr) == 0 {
return utf8.RuneCountInString(s) + 1
}
if len(substr) == 1 {
return bytealg.CountString(s, substr[0])
}
n := 0
for {
i := Index(s, substr)
if i == -1 {
return n
}
n++
s = s[i+len(substr):]
}
}
/ Contains reports whether substr is within s.
func Contains(s, substr string) bool {
return Index(s, substr) >= 0
}
/ ContainsAny reports whether any Unicode code points in chars are within s.
func ContainsAny(s, chars string) bool {
return IndexAny(s, chars) >= 0
}
/ ContainsRune reports whether the Unicode code point r is within s.
func ContainsRune(s string, r rune) bool {
return IndexRune(s, r) >= 0
}
/ LastIndex returns the index of the last instance of substr in s, or -1 if substr is not present in s.
func LastIndex(s, substr string) int {
n := len(substr)
switch {
case n == 0:
return len(s)
case n == 1:
return LastIndexByte(s, substr[0])
case n == len(s):
if substr == s {
return 0
}
return -1
case n > len(s):
return -1
}
/ Rabin-Karp search from the end of the string
hashss, pow := bytealg.HashStrRev(substr)
last := len(s) - n
var h uint32
for i := len(s) - 1; i >= last; i-- {
h = h*bytealg.PrimeRK + uint32(s[i])
}
if h == hashss && s[last:] == substr {
return last
}
for i := last - 1; i >= 0; i-- {
h *= bytealg.PrimeRK
h += uint32(s[i])
h -= pow * uint32(s[i+n])
if h == hashss && s[i:i+n] == substr {
return i
}
}
return -1
}
/ IndexByte returns the index of the first instance of c in s, or -1 if c is not present in s.
func IndexByte(s string, c byte) int {
return bytealg.IndexByteString(s, c)
}
/ IndexRune returns the index of the first instance of the Unicode code point
/ r, or -1 if rune is not present in s.
/ If r is utf8.RuneError, it returns the first instance of any
/ invalid UTF-8 byte sequence.
func IndexRune(s string, r rune) int {
switch {
case 0 <= r && r < utf8.RuneSelf:
return IndexByte(s, byte(r))
case r == utf8.RuneError:
for i, r := range s {
if r == utf8.RuneError {
return i
}
}
return -1
case !utf8.ValidRune(r):
return -1
default:
return Index(s, string(r))
}
}
/ 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 chars == "" {
/ Avoid scanning all of s.
return -1
}
if len(chars) == 1 {
/ Avoid scanning all of s.
r := rune(chars[0])
if r >= utf8.RuneSelf {
r = utf8.RuneError
}
return IndexRune(s, r)
}
if len(s) > 8 {
if as, isASCII := makeASCIISet(chars); isASCII {
for i := 0; i < len(s); i++ {
if as.contains(s[i]) {
return i
}
}
return -1
}
}
for i, c := range s {
if IndexRune(chars, c) >= 0 {
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 chars == "" {
/ Avoid scanning all of s.
return -1
}
if len(s) == 1 {
rc := rune(s[0])
if rc >= utf8.RuneSelf {
rc = utf8.RuneError
}
if IndexRune(chars, rc) >= 0 {
return 0
}
return -1
}
if len(s) > 8 {
if as, isASCII := makeASCIISet(chars); isASCII {
for i := len(s) - 1; i >= 0; i-- {
if as.contains(s[i]) {
return i
}
}
return -1
}
}
if len(chars) == 1 {
rc := rune(chars[0])
if rc >= utf8.RuneSelf {
rc = utf8.RuneError
}
for i := len(s); i > 0; {
r, size := utf8.DecodeLastRuneInString(s[:i])
i -= size
if rc == r {
return i
}
}
return -1
}
for i := len(s); i > 0; {
r, size := utf8.DecodeLastRuneInString(s[:i])
i -= size
if IndexRune(chars, r) >= 0 {
return i
}
}
return -1
}
/ LastIndexByte returns the index of the last instance of c in s, or -1 if c is not present in s.
func LastIndexByte(s string, c byte) int {
for i := len(s) - 1; i >= 0; i-- {
if s[i] == c {
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
}
if n > len(s)+1 {
n = len(s) + 1
}
a := make([]string, n)
n--
i := 0
for i < n {
m := Index(s, sep)
if m < 0 {
break
}
a[i] = s[:m+sepSave]
s = s[m+len(sep):]
i++
}
a[i] = s
return a[:i+1]
}
/ SplitN slices s into substrings separated by sep and returns a slice of
/ the substrings between those separators.
/
/ 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
/
/ Edge cases for s and sep (for example, empty strings) are handled
/ as described in the documentation for Split.
/
/ To split around the first instance of a separator, see Cut.
func SplitN(s, sep string, n int) []string { return genSplit(s, sep, 0, n) }
/ SplitAfterN slices s into substrings after each instance of sep and
/ returns a slice of those substrings.
/
/ 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
/
/ Edge cases for s and sep (for example, empty strings) are handled
/ as described in the documentation for SplitAfter.
func SplitAfterN(s, sep string, n int) []string {
return genSplit(s, sep, len(sep), n)
}
/ Split slices s into all substrings separated by sep and returns a slice of
/ the substrings between those separators.
/
/ If s does not contain sep and sep is not empty, Split returns a
/ slice of length 1 whose only element is s.
/
/ If sep is empty, Split splits after each UTF-8 sequence. If both s
/ and sep are empty, Split returns an empty slice.
/
/ It is equivalent to SplitN with a count of -1.
/
/ To split around the first instance of a separator, see Cut.
func Split(s, sep string) []string { return genSplit(s, sep, 0, -1) }
/ SplitAfter slices s into all substrings after each instance of sep and
/ returns a slice of those substrings.
/
/ If s does not contain sep and sep is not empty, SplitAfter returns
/ a slice of length 1 whose only element is s.
/
/ If sep is empty, SplitAfter splits after each UTF-8 sequence. If
/ both s and sep are empty, SplitAfter returns an empty slice.
/
/ It is equivalent to SplitAfterN with a count of -1.
func SplitAfter(s, sep string) []string {
return genSplit(s, sep, len(sep), -1)
}
var asciiSpace = [256]uint8{'\t': 1, '\n': 1, '\v': 1, '\f': 1, '\r': 1, ' ': 1}
/ Fields splits the string s around each instance of one or more consecutive white space
/ characters, as defined by unicode.IsSpace, returning a slice of substrings of s or an
/ empty slice if s contains only white space.
func Fields(s string) []string {
/ First count the fields.
/ This is an exact count if s is ASCII, otherwise it is an approximation.
n := 0
wasSpace := 1
/ setBits is used to track which bits are set in the bytes of s.
setBits := uint8(0)
for i := 0; i < len(s); i++ {
r := s[i]
setBits |= r
isSpace := int(asciiSpace[r])
n += wasSpace & ^isSpace
wasSpace = isSpace
}
if setBits >= utf8.RuneSelf {
/ Some runes in the input string are not ASCII.
return FieldsFunc(s, unicode.IsSpace)
}
/ ASCII fast path
a := make([]string, n)
na := 0
fieldStart := 0
i := 0
/ Skip spaces in the front of the input.
for i < len(s) && asciiSpace[s[i]] != 0 {
i++
}
fieldStart = i
for i < len(s) {
if asciiSpace[s[i]] == 0 {
i++
continue
}
a[na] = s[fieldStart:i]
na++
i++
/ Skip spaces in between fields.
for i < len(s) && asciiSpace[s[i]] != 0 {
i++
}
fieldStart = i
}
if fieldStart < len(s) { / Last field might end at EOF.
a[na] = s[fieldStart:]
}
return a
}
/ 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.
/
/ FieldsFunc makes no guarantees about the order in which it calls f(c)
/ and assumes that f always returns the same value for a given c.
func FieldsFunc(s string, f func(rune) bool) []string {
/ A span is used to record a slice of s of the form s[start:end].
/ The start index is inclusive and the end index is exclusive.
type span struct {
start int
end int
}
spans := make([]span, 0, 32)
/ Find the field start and end indices.
/ Doing this in a separate pass (rather than slicing the string s
/ and collecting the result substrings right away) is significantly
/ more efficient, possibly due to cache effects.
start := -1 / valid span start if >= 0
for end, rune := range s {
if f(rune) {
if start >= 0 {
spans = append(spans, span{start, end})
/ Set start to a negative value.
/ Note: using -1 here consistently and reproducibly
/ slows down this code by a several percent on amd64.
start = ^start
}
} else {
if start < 0 {
start = end
}
}
}
/ Last field might end at EOF.
if start >= 0 {
spans = append(spans, span{start, len(s)})
}
/ Create strings from recorded field indices.
a := make([]string, len(spans))
for i, span := range spans {
a[i] = s[span.start:span.end]
}
return a
}
/ Join concatenates the elements of its first argument to create a single string. The separator
/ string sep is placed between elements in the resulting string.
func Join(elems []string, sep string) string {
switch len(elems) {
case 0:
return ""
case 1:
return elems[0]
}
n := len(sep) * (len(elems) - 1)
for i := 0; i < len(elems); i++ {
n += len(elems[i])
}
var b Builder
b.Grow(n)
b.WriteString(elems[0])
for _, s := range elems[1:] {
b.WriteString(sep)
b.WriteString(s)
}
return b.String()
}
/ 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) rune, 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.
/ The output buffer b is initialized on demand, the first
/ time a character differs.
var b Builder
for i, c := range s {
r := mapping(c)
if r == c && c != utf8.RuneError {
continue
}
var width int
if c == utf8.RuneError {
c, width = utf8.DecodeRuneInString(s[i:])
if width != 1 && r == c {
continue
}
} else {
width = utf8.RuneLen(c)
}
b.Grow(len(s) + utf8.UTFMax)
b.WriteString(s[:i])
if r >= 0 {
b.WriteRune(r)
}
s = s[i+width:]
break
}
/ Fast path for unchanged input
if b.Cap() == 0 { / didn't call b.Grow above
return s
}
for _, c := range s {
r := mapping(c)
if r >= 0 {
/ common case
/ Due to inlining, it is more performant to determine if WriteByte should be
/ invoked rather than always call WriteRune
if r < utf8.RuneSelf {
b.WriteByte(byte(r))
} else {
/ r is not a ASCII rune.
b.WriteRune(r)
}
}
}
return b.String()
}
/ Repeat returns a new string consisting of count copies of the string s.
/
/ It panics if count is negative or if
/ the result of (len(s) * count) overflows.
func Repeat(s string, count int) string {
if count == 0 {
return ""
}
/ Since we cannot return an error on overflow,
/ we should panic if the repeat will generate
/ an overflow.
/ See Issue golang.org/issue/16237
if count < 0 {
panic("strings: negative Repeat count")
} else if len(s)*count/count != len(s) {
panic("strings: Repeat count causes overflow")
}
n := len(s) * count
var b Builder
b.Grow(n)
b.WriteString(s)
for b.Len() < n {
if b.Len() <= n/2 {
b.WriteString(b.String())
} else {
b.WriteString(b.String()[:n-b.Len()])
break
}
}
return b.String()
}
/ ToUpper returns s with all Unicode letters mapped to their upper case.
func ToUpper(s string) string {
isASCII, hasLower := true, false
for i := 0; i < len(s); i++ {
c := s[i]
if c >= utf8.RuneSelf {
isASCII = false
break
}
hasLower = hasLower || ('a' <= c && c <= 'z')
}
if isASCII { / optimize for ASCII-only strings.
if !hasLower {
return s
}
var b Builder
b.Grow(len(s))
for i := 0; i < len(s); i++ {
c := s[i]
if 'a' <= c && c <= 'z' {
c -= 'a' - 'A'
}
b.WriteByte(c)
}
return b.String()
}
return Map(unicode.ToUpper, s)
}
/ ToLower returns s with all Unicode letters mapped to their lower case.
func ToLower(s string) string {
isASCII, hasUpper := true, false
for i := 0; i < len(s); i++ {
c := s[i]
if c >= utf8.RuneSelf {
isASCII = false
break
}
hasUpper = hasUpper || ('A' <= c && c <= 'Z')
}
if isASCII { / optimize for ASCII-only strings.
if !hasUpper {
return s
}
var b Builder
b.Grow(len(s))
for i := 0; i < len(s); i++ {
c := s[i]
if 'A' <= c && c <= 'Z' {
c += 'a' - 'A'
}
b.WriteByte(c)
}
return b.String()
}
return Map(unicode.ToLower, s)
}
/ ToTitle returns a copy of the string s with all Unicode letters mapped to
/ their Unicode 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 using the case mapping specified by c.
func ToUpperSpecial(c unicode.SpecialCase, s string) string {
return Map(c.ToUpper, s)
}
/ ToLowerSpecial returns a copy of the string s with all Unicode letters mapped to their
/ lower case using the case mapping specified by c.
func ToLowerSpecial(c unicode.SpecialCase, s string) string {
return Map(c.ToLower, s)
}
/ ToTitleSpecial returns a copy of the string s with all Unicode letters mapped to their
/ Unicode title case, giving priority to the special casing rules.
func ToTitleSpecial(c unicode.SpecialCase, s string) string {
return Map(c.ToTitle, s)
}
/ ToValidUTF8 returns a copy of the string s with each run of invalid UTF-8 byte sequences
/ replaced by the replacement string, which may be empty.
func ToValidUTF8(s, replacement string) string {
var b Builder
for i, c := range s {
if c != utf8.RuneError {
continue
}
_, wid := utf8.DecodeRuneInString(s[i:])
if wid == 1 {
b.Grow(len(s) + len(replacement))
b.WriteString(s[:i])
s = s[i:]
break
}
}
/ Fast path for unchanged input
if b.Cap() == 0 { / didn't call b.Grow above
return s
}
invalid := false / previous byte was from an invalid UTF-8 sequence
for i := 0; i < len(s); {
c := s[i]
if c < utf8.RuneSelf {
i++
invalid = false
b.WriteByte(c)
continue
}
_, wid := utf8.DecodeRuneInString(s[i:])
if wid == 1 {
i++
if !invalid {
invalid = true
b.WriteString(replacement)
}
continue
}
invalid = false
b.WriteString(s[i : i+wid])
i += wid
}
return b.String()
}
/ isSeparator reports whether the rune could mark a word boundary.
/ TODO: update when package unicode captures more of the properties.
func isSeparator(r rune) bool {
/ ASCII alphanumerics and underscore are not separators
if r <= 0x7F {
switch {
case '0' <= r && r <= '9':
return false
case 'a' <= r && r <= 'z':
return false
case 'A' <= r && r <= 'Z':
return false
case r == '_':
return false
}
return true
}
/ Letters and digits are not separators
if unicode.IsLetter(r) || unicode.IsDigit(r) {
return false
}
/ Otherwise, all we can do for now is treat spaces as separators.
return unicode.IsSpace(r)
}
/ Title returns a copy of the string s with all Unicode letters that begin words
/ mapped to their Unicode title case.
/
/ Deprecated: The rule Title uses for word boundaries does not handle Unicode
/ punctuation properly. Use golang.org/x/text/cases instead.
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 rune) rune {
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(rune) 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(rune) 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(rune) 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(rune) 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(rune) 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(rune) bool, truth bool) int {
for i, r := range s {
if f(r) == truth {
return i
}
}
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(rune) bool, truth bool) int {
for i := len(s); i > 0; {
r, size := utf8.DecodeLastRuneInString(s[0:i])
i -= size
if f(r) == truth {
return i
}
}
return -1
}
/ asciiSet is a 32-byte value, where each bit represents the presence of a
/ given ASCII character in the set. The 128-bits of the lower 16 bytes,
/ starting with the least-significant bit of the lowest word to the
/ most-significant bit of the highest word, map to the full range of all
/ 128 ASCII characters. The 128-bits of the upper 16 bytes will be zeroed,
/ ensuring that any non-ASCII character will be reported as not in the set.
/ This allocates a total of 32 bytes even though the upper half
/ is unused to avoid bounds checks in asciiSet.contains.
type asciiSet [8]uint32
/ makeASCIISet creates a set of ASCII characters and reports whether all
/ characters in chars are ASCII.
func makeASCIISet(chars string) (as asciiSet, ok bool) {
for i := 0; i < len(chars); i++ {
c := chars[i]
if c >= utf8.RuneSelf {
return as, false
}
as[c/32] |= 1 << (c % 32)
}
return as, true
}
/ contains reports whether c is inside the set.
func (as *asciiSet) contains(c byte) bool {
return (as[c/32] & (1 << (c % 32))) != 0
}
/ Trim returns a slice of the string s with all leading and
/ trailing Unicode code points contained in cutset removed.
func Trim(s, cutset string) string {
if s == "" || cutset == "" {
return s
}
if len(cutset) == 1 && cutset[0] < utf8.RuneSelf {
return trimLeftByte(trimRightByte(s, cutset[0]), cutset[0])
}
if as, ok := makeASCIISet(cutset); ok {
return trimLeftASCII(trimRightASCII(s, &as), &as)
}
return trimLeftUnicode(trimRightUnicode(s, cutset), cutset)
}
/ TrimLeft returns a slice of the string s with all leading
/ Unicode code points contained in cutset removed.
/
/ To remove a prefix, use TrimPrefix instead.
func TrimLeft(s, cutset string) string {
if s == "" || cutset == "" {
return s
}
if len(cutset) == 1 && cutset[0] < utf8.RuneSelf {
return trimLeftByte(s, cutset[0])
}
if as, ok := makeASCIISet(cutset); ok {
return trimLeftASCII(s, &as)
}
return trimLeftUnicode(s, cutset)
}
func trimLeftByte(s string, c byte) string {
for len(s) > 0 && s[0] == c {
s = s[1:]
}
return s
}
func trimLeftASCII(s string, as *asciiSet) string {
for len(s) > 0 {
if !as.contains(s[0]) {
break
}
s = s[1:]
}
return s
}
func trimLeftUnicode(s, cutset string) string {
for len(s) > 0 {
r, n := rune(s[0]), 1
if r >= utf8.RuneSelf {
r, n = utf8.DecodeRuneInString(s)
}
if !ContainsRune(cutset, r) {
break
}
s = s[n:]
}
return s
}
/ TrimRight returns a slice of the string s, with all trailing
/ Unicode code points contained in cutset removed.
/
/ To remove a suffix, use TrimSuffix instead.
func TrimRight(s, cutset string) string {
if s == "" || cutset == "" {
return s
}
if len(cutset) == 1 && cutset[0] < utf8.RuneSelf {
return trimRightByte(s, cutset[0])
}
if as, ok := makeASCIISet(cutset); ok {
return trimRightASCII(s, &as)
}
return trimRightUnicode(s, cutset)
}
func trimRightByte(s string, c byte) string {
for len(s) > 0 && s[len(s)-1] == c {
s = s[:len(s)-1]
}
return s
}
func trimRightASCII(s string, as *asciiSet) string {
for len(s) > 0 {
if !as.contains(s[len(s)-1]) {
break
}
s = s[:len(s)-1]
}
return s
}
func trimRightUnicode(s, cutset string) string {
for len(s) > 0 {
r, n := rune(s[len(s)-1]), 1
if r >= utf8.RuneSelf {
r, n = utf8.DecodeLastRuneInString(s)
}
if !ContainsRune(cutset, r) {
break
}
s = s[:len(s)-n]
}
return s
}
/ 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 {
/ Fast path for ASCII: look for the first ASCII non-space byte
start := 0
for ; start < len(s); start++ {
c := s[start]
if c >= utf8.RuneSelf {
/ If we run into a non-ASCII byte, fall back to the
/ slower unicode-aware method on the remaining bytes
return TrimFunc(s[start:], unicode.IsSpace)
}
if asciiSpace[c] == 0 {
break
}
}
/ Now look for the first ASCII non-space byte from the end
stop := len(s)
for ; stop > start; stop-- {
c := s[stop-1]
if c >= utf8.RuneSelf {
/ start has been already trimmed above, should trim end only
return TrimRightFunc(s[start:stop], unicode.IsSpace)
}
if asciiSpace[c] == 0 {
break
}
}
/ At this point s[start:stop] starts and ends with an ASCII
/ non-space bytes, so we're done. Non-ASCII cases have already
/ been handled above.
return s[start:stop]
}
/ TrimPrefix returns s without the provided leading prefix string.
/ If s doesn't start with prefix, s is returned unchanged.
func TrimPrefix(s, prefix string) string {
if HasPrefix(s, prefix) {
return s[len(prefix):]
}
return s
}
/ TrimSuffix returns s without the provided trailing suffix string.
/ If s doesn't end with suffix, s is returned unchanged.
func TrimSuffix(s, suffix string) string {
if HasSuffix(s, suffix) {
return s[:len(s)-len(suffix)]
}
return s
}
/ Replace returns a copy of the string s with the first n
/ non-overlapping instances of old replaced by new.
/ If old is empty, it matches at the beginning of the string
/ and after each UTF-8 sequence, yielding up to k+1 replacements
/ for a k-rune string.
/ 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.
var b Builder
b.Grow(len(s) + n*(len(new)-len(old)))
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)
}
b.WriteString(s[start:j])
b.WriteString(new)
start = j + len(old)
}
b.WriteString(s[start:])
return b.String()
}
/ ReplaceAll returns a copy of the string s with all
/ non-overlapping instances of old replaced by new.
/ If old is empty, it matches at the beginning of the string
/ and after each UTF-8 sequence, yielding up to k+1 replacements
/ for a k-rune string.
func ReplaceAll(s, old, new string) string {
return Replace(s, old, new, -1)
}
/ EqualFold reports whether s and t, interpreted as UTF-8 strings,
/ are equal under simple Unicode case-folding, which is a more general
/ form of case-insensitivity.
func EqualFold(s, t string) bool {
for s != "" && t != "" {
/ Extract first rune from each string.
var sr, tr rune
if s[0] < utf8.RuneSelf {
sr, s = rune(s[0]), s[1:]
} else {
r, size := utf8.DecodeRuneInString(s)
sr, s = r, s[size:]
}
if t[0] < utf8.RuneSelf {
tr, t = rune(t[0]), t[1:]
} else {
r, size := utf8.DecodeRuneInString(t)
tr, t = r, t[size:]
}
/ If they match, keep going; if not, return false.
/ Easy case.
if tr == sr {
continue
}
/ Make sr < tr to simplify what follows.
if tr < sr {
tr, sr = sr, tr
}
/ Fast check for ASCII.
if tr < utf8.RuneSelf {
/ ASCII only, sr/tr must be upper/lower case
if 'A' <= sr && sr <= 'Z' && tr == sr+'a'-'A' {
continue
}
return false
}
/ General case. SimpleFold(x) returns the next equivalent rune > x
/ or wraps around to smaller values.
r := unicode.SimpleFold(sr)
for r != sr && r < tr {
r = unicode.SimpleFold(r)
}
if r == tr {
continue
}
return false
}
/ One string is empty. Are both?
return s == t
}
/ Index returns the index of the first instance of substr in s, or -1 if substr is not present in s.
func Index(s, substr string) int {
n := len(substr)
switch {
case n == 0:
return 0
case n == 1:
return IndexByte(s, substr[0])
case n == len(s):
if substr == s {
return 0
}
return -1
case n > len(s):
return -1
case n <= bytealg.MaxLen:
/ Use brute force when s and substr both are small
if len(s) <= bytealg.MaxBruteForce {
return bytealg.IndexString(s, substr)
}
c0 := substr[0]
c1 := substr[1]
i := 0
t := len(s) - n + 1
fails := 0
for i < t {
if s[i] != c0 {
/ IndexByte is faster than bytealg.IndexString, so use it as long as
/ we're not getting lots of false positives.
o := IndexByte(s[i+1:t], c0)
if o < 0 {
return -1
}
i += o + 1
}
if s[i+1] == c1 && s[i:i+n] == substr {
return i
}
fails++
i++
/ Switch to bytealg.IndexString when IndexByte produces too many false positives.
if fails > bytealg.Cutover(i) {
r := bytealg.IndexString(s[i:], substr)
if r >= 0 {
return r + i
}
return -1
}
}
return -1
}
c0 := substr[0]
c1 := substr[1]
i := 0
t := len(s) - n + 1
fails := 0
for i < t {
if s[i] != c0 {
o := IndexByte(s[i+1:t], c0)
if o < 0 {
return -1
}
i += o + 1
}
if s[i+1] == c1 && s[i:i+n] == substr {
return i
}
i++
fails++
if fails >= 4+i>>4 && i < t {
/ See comment in ../bytes/bytes.go.
j := bytealg.IndexRabinKarp(s[i:], substr)
if j < 0 {
return -1
}
return i + j
}
}
return -1
}
/ Cut slices s around the first instance of sep,
/ returning the text before and after sep.
/ The found result reports whether sep appears in s.
/ If sep does not appear in s, cut returns s, "", false.
func Cut(s, sep string) (before, after string, found bool) {
if i := Index(s, sep); i >= 0 {
return s[:i], s[i+len(sep):], true
}
return s, "", false
}