// 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" ) const maxInt = int(^uint(0) >> 1) // 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 bytes are sliced individually. 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++ { _, size := utf8.DecodeRuneInString(s) a[i] = s[:size] s = s[size:] } 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 } // ContainsFunc reports whether any Unicode code points r within s satisfy f(r). func ContainsFunc(s string, f func(rune) bool) bool { return IndexFunc(s, f) >= 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 bytealg.LastIndexByteString(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 { return bytealg.LastIndexByteString(s, c) } // 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] } var n int if len(sep) > 0 { if len(sep) >= maxInt/(len(elems)-1) { panic("strings: Join output length overflow") } n += len(sep) * (len(elems) - 1) } for _, elem := range elems { if len(elem) > maxInt-n { panic("strings: Join output length overflow") } n += len(elem) } 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 reports whether the string s begins with prefix. func HasPrefix(s, prefix string) bool { return len(s) >= len(prefix) && s[0:len(prefix)] == prefix } // HasSuffix reports 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 an 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 { switch count { case 0: return "" case 1: return s } // Since we cannot return an error on overflow, // we should panic if the repeat will generate an overflow. // See golang.org/issue/16237. if count < 0 { panic("strings: negative Repeat count") } if len(s) >= maxInt/count { panic("strings: Repeat output length overflow") } n := len(s) * count if len(s) == 0 { return "" } // Past a certain chunk size it is counterproductive to use // larger chunks as the source of the write, as when the source // is too large we are basically just thrashing the CPU D-cache. // So if the result length is larger than an empirically-found // limit (8KB), we stop growing the source string once the limit // is reached and keep reusing the same source string - that // should therefore be always resident in the L1 cache - until we // have completed the construction of the result. // This yields significant speedups (up to +100%) in cases where // the result length is large (roughly, over L2 cache size). const chunkLimit = 8 * 1024 chunkMax := n if n > chunkLimit { chunkMax = chunkLimit / len(s) * len(s) if chunkMax == 0 { chunkMax = len(s) } } var b Builder b.Grow(n) b.WriteString(s) for b.Len() < n { chunk := n - b.Len() if chunk > b.Len() { chunk = b.Len() } if chunk > chunkMax { chunk = chunkMax } b.WriteString(b.String()[:chunk]) } 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 pos int ) b.Grow(len(s)) for i := 0; i < len(s); i++ { c := s[i] if 'a' <= c && c <= 'z' { c -= 'a' - 'A' if pos < i { b.WriteString(s[pos:i]) } b.WriteByte(c) pos = i + 1 } } if pos < len(s) { b.WriteString(s[pos:]) } 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 pos int ) b.Grow(len(s)) for i := 0; i < len(s); i++ { c := s[i] if 'A' <= c && c <= 'Z' { c += 'a' - 'A' if pos < i { b.WriteString(s[pos:i]) } b.WriteByte(c) pos = i + 1 } } if pos < len(s) { b.WriteString(s[pos:]) } 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 { // ASCII fast path i := 0 for ; i < len(s) && i < len(t); i++ { sr := s[i] tr := t[i] if sr|tr >= utf8.RuneSelf { goto hasUnicode } // Easy case. if tr == sr { continue } // Make sr < tr to simplify what follows. if tr < sr { tr, sr = sr, tr } // ASCII only, sr/tr must be upper/lower case if 'A' <= sr && sr <= 'Z' && tr == sr+'a'-'A' { continue } return false } // Check if we've exhausted both strings. return len(s) == len(t) hasUnicode: s = s[i:] t = t[i:] for _, sr := range s { // If t is exhausted the strings are not equal. if len(t) == 0 { return false } // Extract first rune from second string. var tr rune 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 } // First string is empty, so check if the second one is also empty. return len(t) == 0 } // 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 } // CutPrefix returns s without the provided leading prefix string // and reports whether it found the prefix. // If s doesn't start with prefix, CutPrefix returns s, false. // If prefix is the empty string, CutPrefix returns s, true. func CutPrefix(s, prefix string) (after string, found bool) { if !HasPrefix(s, prefix) { return s, false } return s[len(prefix):], true } // CutSuffix returns s without the provided ending suffix string // and reports whether it found the suffix. // If s doesn't end with suffix, CutSuffix returns s, false. // If suffix is the empty string, CutSuffix returns s, true. func CutSuffix(s, suffix string) (before string, found bool) { if !HasSuffix(s, suffix) { return s, false } return s[:len(s)-len(suffix)], true }