| // 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 |
| 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 |
| } |
| |
| // 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 |
| } |
| |
| // 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 splits the string s around each instance of sep, returning an array of substrings of s. |
| // If sep is empty, Split splits s after each UTF-8 sequence. |
| // If n >= 0, Split splits s into at most n substrings; the last substring will be the unsplit remainder. |
| // Thus if n == 0, the result will be nil. |
| func Split(s, sep string, n int) []string { return genSplit(s, sep, 0, n) } |
| |
| // SplitAfter splits the string s after each instance of sep, returning an array of substrings of s. |
| // If sep is empty, SplitAfter splits s after each UTF-8 sequence. |
| // If n >= 0, SplitAfter splits s into at most n substrings; the last substring will be the unsplit remainder. |
| // Thus if n == 0, the result will be nil. |
| 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 satifying f(c) |
| // and returns an array of slices of s. If no code points in s satisfy f(c), 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(rune, b[nbytes:maxbytes]) |
| } |
| } |
| 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) |
| } |
| |
| // 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. We could use IndexFunc directly, but this |
| // way saves a closure allocation. |
| 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. We could use IndexFunc directly, but this |
| // way saves a closure allocation. |
| func lastIndexFunc(s string, f func(r int) bool, truth bool) int { |
| end := len(s) |
| for end > 0 { |
| start := end - 1 |
| rune := int(s[start]) |
| if rune >= utf8.RuneSelf { |
| // Back up & look for beginning of rune. Mustn't pass start. |
| for start--; start >= 0; start-- { |
| if utf8.RuneStart(s[start]) { |
| break |
| } |
| } |
| if start < 0 { |
| return -1 |
| } |
| var wid int |
| rune, wid = utf8.DecodeRuneInString(s[start:end]) |
| |
| // If we've decoded fewer bytes than we expected, |
| // we've got some invalid UTF-8, so make sure we return |
| // the last possible index in s. |
| if start+wid < end && f(utf8.RuneError) == truth { |
| return end - 1 |
| } |
| } |
| if f(rune) == truth { |
| return start |
| } |
| end = start |
| } |
| 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 += copyString(t[w:], s[start:j]) |
| w += copyString(t[w:], new) |
| start = j + len(old) |
| } |
| w += copyString(t[w:], s[start:]) |
| return string(t[0:w]) |
| } |
| |
| func copyString(dst []byte, src string) int { |
| n := len(dst) |
| if n > len(src) { |
| n = len(src) |
| } |
| for i := 0; i < n; i++ { |
| dst[i] = src[i] |
| } |
| return n |
| } |