Source file src/strings/strings.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package strings implements simple functions to manipulate UTF-8 encoded strings.
     6  //
     7  // For information about UTF-8 strings in Go, see https://blog.golang.org/strings.
     8  package strings
     9  
    10  import (
    11  	"internal/bytealg"
    12  	"internal/stringslite"
    13  	"unicode"
    14  	"unicode/utf8"
    15  )
    16  
    17  const maxInt = int(^uint(0) >> 1)
    18  
    19  // explode splits s into a slice of UTF-8 strings,
    20  // one string per Unicode character up to a maximum of n (n < 0 means no limit).
    21  // Invalid UTF-8 bytes are sliced individually.
    22  func explode(s string, n int) []string {
    23  	l := utf8.RuneCountInString(s)
    24  	if n < 0 || n > l {
    25  		n = l
    26  	}
    27  	a := make([]string, n)
    28  	for i := 0; i < n-1; i++ {
    29  		_, size := utf8.DecodeRuneInString(s)
    30  		a[i] = s[:size]
    31  		s = s[size:]
    32  	}
    33  	if n > 0 {
    34  		a[n-1] = s
    35  	}
    36  	return a
    37  }
    38  
    39  // Count counts the number of non-overlapping instances of substr in s.
    40  // If substr is an empty string, Count returns 1 + the number of Unicode code points in s.
    41  func Count(s, substr string) int {
    42  	// special case
    43  	if len(substr) == 0 {
    44  		return utf8.RuneCountInString(s) + 1
    45  	}
    46  	if len(substr) == 1 {
    47  		return bytealg.CountString(s, substr[0])
    48  	}
    49  	n := 0
    50  	for {
    51  		i := Index(s, substr)
    52  		if i == -1 {
    53  			return n
    54  		}
    55  		n++
    56  		s = s[i+len(substr):]
    57  	}
    58  }
    59  
    60  // Contains reports whether substr is within s.
    61  func Contains(s, substr string) bool {
    62  	return Index(s, substr) >= 0
    63  }
    64  
    65  // ContainsAny reports whether any Unicode code points in chars are within s.
    66  func ContainsAny(s, chars string) bool {
    67  	return IndexAny(s, chars) >= 0
    68  }
    69  
    70  // ContainsRune reports whether the Unicode code point r is within s.
    71  func ContainsRune(s string, r rune) bool {
    72  	return IndexRune(s, r) >= 0
    73  }
    74  
    75  // ContainsFunc reports whether any Unicode code points r within s satisfy f(r).
    76  func ContainsFunc(s string, f func(rune) bool) bool {
    77  	return IndexFunc(s, f) >= 0
    78  }
    79  
    80  // LastIndex returns the index of the last instance of substr in s, or -1 if substr is not present in s.
    81  func LastIndex(s, substr string) int {
    82  	n := len(substr)
    83  	switch {
    84  	case n == 0:
    85  		return len(s)
    86  	case n == 1:
    87  		return bytealg.LastIndexByteString(s, substr[0])
    88  	case n == len(s):
    89  		if substr == s {
    90  			return 0
    91  		}
    92  		return -1
    93  	case n > len(s):
    94  		return -1
    95  	}
    96  	// Rabin-Karp search from the end of the string
    97  	hashss, pow := bytealg.HashStrRev(substr)
    98  	last := len(s) - n
    99  	var h uint32
   100  	for i := len(s) - 1; i >= last; i-- {
   101  		h = h*bytealg.PrimeRK + uint32(s[i])
   102  	}
   103  	if h == hashss && s[last:] == substr {
   104  		return last
   105  	}
   106  	for i := last - 1; i >= 0; i-- {
   107  		h *= bytealg.PrimeRK
   108  		h += uint32(s[i])
   109  		h -= pow * uint32(s[i+n])
   110  		if h == hashss && s[i:i+n] == substr {
   111  			return i
   112  		}
   113  	}
   114  	return -1
   115  }
   116  
   117  // IndexByte returns the index of the first instance of c in s, or -1 if c is not present in s.
   118  func IndexByte(s string, c byte) int {
   119  	return stringslite.IndexByte(s, c)
   120  }
   121  
   122  // IndexRune returns the index of the first instance of the Unicode code point
   123  // r, or -1 if rune is not present in s.
   124  // If r is [utf8.RuneError], it returns the first instance of any
   125  // invalid UTF-8 byte sequence.
   126  func IndexRune(s string, r rune) int {
   127  	switch {
   128  	case 0 <= r && r < utf8.RuneSelf:
   129  		return IndexByte(s, byte(r))
   130  	case r == utf8.RuneError:
   131  		for i, r := range s {
   132  			if r == utf8.RuneError {
   133  				return i
   134  			}
   135  		}
   136  		return -1
   137  	case !utf8.ValidRune(r):
   138  		return -1
   139  	default:
   140  		return Index(s, string(r))
   141  	}
   142  }
   143  
   144  // IndexAny returns the index of the first instance of any Unicode code point
   145  // from chars in s, or -1 if no Unicode code point from chars is present in s.
   146  func IndexAny(s, chars string) int {
   147  	if chars == "" {
   148  		// Avoid scanning all of s.
   149  		return -1
   150  	}
   151  	if len(chars) == 1 {
   152  		// Avoid scanning all of s.
   153  		r := rune(chars[0])
   154  		if r >= utf8.RuneSelf {
   155  			r = utf8.RuneError
   156  		}
   157  		return IndexRune(s, r)
   158  	}
   159  	if len(s) > 8 {
   160  		if as, isASCII := makeASCIISet(chars); isASCII {
   161  			for i := 0; i < len(s); i++ {
   162  				if as.contains(s[i]) {
   163  					return i
   164  				}
   165  			}
   166  			return -1
   167  		}
   168  	}
   169  	for i, c := range s {
   170  		if IndexRune(chars, c) >= 0 {
   171  			return i
   172  		}
   173  	}
   174  	return -1
   175  }
   176  
   177  // LastIndexAny returns the index of the last instance of any Unicode code
   178  // point from chars in s, or -1 if no Unicode code point from chars is
   179  // present in s.
   180  func LastIndexAny(s, chars string) int {
   181  	if chars == "" {
   182  		// Avoid scanning all of s.
   183  		return -1
   184  	}
   185  	if len(s) == 1 {
   186  		rc := rune(s[0])
   187  		if rc >= utf8.RuneSelf {
   188  			rc = utf8.RuneError
   189  		}
   190  		if IndexRune(chars, rc) >= 0 {
   191  			return 0
   192  		}
   193  		return -1
   194  	}
   195  	if len(s) > 8 {
   196  		if as, isASCII := makeASCIISet(chars); isASCII {
   197  			for i := len(s) - 1; i >= 0; i-- {
   198  				if as.contains(s[i]) {
   199  					return i
   200  				}
   201  			}
   202  			return -1
   203  		}
   204  	}
   205  	if len(chars) == 1 {
   206  		rc := rune(chars[0])
   207  		if rc >= utf8.RuneSelf {
   208  			rc = utf8.RuneError
   209  		}
   210  		for i := len(s); i > 0; {
   211  			r, size := utf8.DecodeLastRuneInString(s[:i])
   212  			i -= size
   213  			if rc == r {
   214  				return i
   215  			}
   216  		}
   217  		return -1
   218  	}
   219  	for i := len(s); i > 0; {
   220  		r, size := utf8.DecodeLastRuneInString(s[:i])
   221  		i -= size
   222  		if IndexRune(chars, r) >= 0 {
   223  			return i
   224  		}
   225  	}
   226  	return -1
   227  }
   228  
   229  // LastIndexByte returns the index of the last instance of c in s, or -1 if c is not present in s.
   230  func LastIndexByte(s string, c byte) int {
   231  	return bytealg.LastIndexByteString(s, c)
   232  }
   233  
   234  // Generic split: splits after each instance of sep,
   235  // including sepSave bytes of sep in the subarrays.
   236  func genSplit(s, sep string, sepSave, n int) []string {
   237  	if n == 0 {
   238  		return nil
   239  	}
   240  	if sep == "" {
   241  		return explode(s, n)
   242  	}
   243  	if n < 0 {
   244  		n = Count(s, sep) + 1
   245  	}
   246  
   247  	if n > len(s)+1 {
   248  		n = len(s) + 1
   249  	}
   250  	a := make([]string, n)
   251  	n--
   252  	i := 0
   253  	for i < n {
   254  		m := Index(s, sep)
   255  		if m < 0 {
   256  			break
   257  		}
   258  		a[i] = s[:m+sepSave]
   259  		s = s[m+len(sep):]
   260  		i++
   261  	}
   262  	a[i] = s
   263  	return a[:i+1]
   264  }
   265  
   266  // SplitN slices s into substrings separated by sep and returns a slice of
   267  // the substrings between those separators.
   268  //
   269  // The count determines the number of substrings to return:
   270  //   - n > 0: at most n substrings; the last substring will be the unsplit remainder;
   271  //   - n == 0: the result is nil (zero substrings);
   272  //   - n < 0: all substrings.
   273  //
   274  // Edge cases for s and sep (for example, empty strings) are handled
   275  // as described in the documentation for [Split].
   276  //
   277  // To split around the first instance of a separator, see [Cut].
   278  func SplitN(s, sep string, n int) []string { return genSplit(s, sep, 0, n) }
   279  
   280  // SplitAfterN slices s into substrings after each instance of sep and
   281  // returns a slice of those substrings.
   282  //
   283  // The count determines the number of substrings to return:
   284  //   - n > 0: at most n substrings; the last substring will be the unsplit remainder;
   285  //   - n == 0: the result is nil (zero substrings);
   286  //   - n < 0: all substrings.
   287  //
   288  // Edge cases for s and sep (for example, empty strings) are handled
   289  // as described in the documentation for [SplitAfter].
   290  func SplitAfterN(s, sep string, n int) []string {
   291  	return genSplit(s, sep, len(sep), n)
   292  }
   293  
   294  // Split slices s into all substrings separated by sep and returns a slice of
   295  // the substrings between those separators.
   296  //
   297  // If s does not contain sep and sep is not empty, Split returns a
   298  // slice of length 1 whose only element is s.
   299  //
   300  // If sep is empty, Split splits after each UTF-8 sequence. If both s
   301  // and sep are empty, Split returns an empty slice.
   302  //
   303  // It is equivalent to [SplitN] with a count of -1.
   304  //
   305  // To split around the first instance of a separator, see [Cut].
   306  func Split(s, sep string) []string { return genSplit(s, sep, 0, -1) }
   307  
   308  // SplitAfter slices s into all substrings after each instance of sep and
   309  // returns a slice of those substrings.
   310  //
   311  // If s does not contain sep and sep is not empty, SplitAfter returns
   312  // a slice of length 1 whose only element is s.
   313  //
   314  // If sep is empty, SplitAfter splits after each UTF-8 sequence. If
   315  // both s and sep are empty, SplitAfter returns an empty slice.
   316  //
   317  // It is equivalent to [SplitAfterN] with a count of -1.
   318  func SplitAfter(s, sep string) []string {
   319  	return genSplit(s, sep, len(sep), -1)
   320  }
   321  
   322  var asciiSpace = [256]uint8{'\t': 1, '\n': 1, '\v': 1, '\f': 1, '\r': 1, ' ': 1}
   323  
   324  // Fields splits the string s around each instance of one or more consecutive white space
   325  // characters, as defined by [unicode.IsSpace], returning a slice of substrings of s or an
   326  // empty slice if s contains only white space.
   327  func Fields(s string) []string {
   328  	// First count the fields.
   329  	// This is an exact count if s is ASCII, otherwise it is an approximation.
   330  	n := 0
   331  	wasSpace := 1
   332  	// setBits is used to track which bits are set in the bytes of s.
   333  	setBits := uint8(0)
   334  	for i := 0; i < len(s); i++ {
   335  		r := s[i]
   336  		setBits |= r
   337  		isSpace := int(asciiSpace[r])
   338  		n += wasSpace & ^isSpace
   339  		wasSpace = isSpace
   340  	}
   341  
   342  	if setBits >= utf8.RuneSelf {
   343  		// Some runes in the input string are not ASCII.
   344  		return FieldsFunc(s, unicode.IsSpace)
   345  	}
   346  	// ASCII fast path
   347  	a := make([]string, n)
   348  	na := 0
   349  	fieldStart := 0
   350  	i := 0
   351  	// Skip spaces in the front of the input.
   352  	for i < len(s) && asciiSpace[s[i]] != 0 {
   353  		i++
   354  	}
   355  	fieldStart = i
   356  	for i < len(s) {
   357  		if asciiSpace[s[i]] == 0 {
   358  			i++
   359  			continue
   360  		}
   361  		a[na] = s[fieldStart:i]
   362  		na++
   363  		i++
   364  		// Skip spaces in between fields.
   365  		for i < len(s) && asciiSpace[s[i]] != 0 {
   366  			i++
   367  		}
   368  		fieldStart = i
   369  	}
   370  	if fieldStart < len(s) { // Last field might end at EOF.
   371  		a[na] = s[fieldStart:]
   372  	}
   373  	return a
   374  }
   375  
   376  // FieldsFunc splits the string s at each run of Unicode code points c satisfying f(c)
   377  // and returns an array of slices of s. If all code points in s satisfy f(c) or the
   378  // string is empty, an empty slice is returned.
   379  //
   380  // FieldsFunc makes no guarantees about the order in which it calls f(c)
   381  // and assumes that f always returns the same value for a given c.
   382  func FieldsFunc(s string, f func(rune) bool) []string {
   383  	// A span is used to record a slice of s of the form s[start:end].
   384  	// The start index is inclusive and the end index is exclusive.
   385  	type span struct {
   386  		start int
   387  		end   int
   388  	}
   389  	spans := make([]span, 0, 32)
   390  
   391  	// Find the field start and end indices.
   392  	// Doing this in a separate pass (rather than slicing the string s
   393  	// and collecting the result substrings right away) is significantly
   394  	// more efficient, possibly due to cache effects.
   395  	start := -1 // valid span start if >= 0
   396  	for end, rune := range s {
   397  		if f(rune) {
   398  			if start >= 0 {
   399  				spans = append(spans, span{start, end})
   400  				// Set start to a negative value.
   401  				// Note: using -1 here consistently and reproducibly
   402  				// slows down this code by a several percent on amd64.
   403  				start = ^start
   404  			}
   405  		} else {
   406  			if start < 0 {
   407  				start = end
   408  			}
   409  		}
   410  	}
   411  
   412  	// Last field might end at EOF.
   413  	if start >= 0 {
   414  		spans = append(spans, span{start, len(s)})
   415  	}
   416  
   417  	// Create strings from recorded field indices.
   418  	a := make([]string, len(spans))
   419  	for i, span := range spans {
   420  		a[i] = s[span.start:span.end]
   421  	}
   422  
   423  	return a
   424  }
   425  
   426  // Join concatenates the elements of its first argument to create a single string. The separator
   427  // string sep is placed between elements in the resulting string.
   428  func Join(elems []string, sep string) string {
   429  	switch len(elems) {
   430  	case 0:
   431  		return ""
   432  	case 1:
   433  		return elems[0]
   434  	}
   435  
   436  	var n int
   437  	if len(sep) > 0 {
   438  		if len(sep) >= maxInt/(len(elems)-1) {
   439  			panic("strings: Join output length overflow")
   440  		}
   441  		n += len(sep) * (len(elems) - 1)
   442  	}
   443  	for _, elem := range elems {
   444  		if len(elem) > maxInt-n {
   445  			panic("strings: Join output length overflow")
   446  		}
   447  		n += len(elem)
   448  	}
   449  
   450  	var b Builder
   451  	b.Grow(n)
   452  	b.WriteString(elems[0])
   453  	for _, s := range elems[1:] {
   454  		b.WriteString(sep)
   455  		b.WriteString(s)
   456  	}
   457  	return b.String()
   458  }
   459  
   460  // HasPrefix reports whether the string s begins with prefix.
   461  func HasPrefix(s, prefix string) bool {
   462  	return stringslite.HasPrefix(s, prefix)
   463  }
   464  
   465  // HasSuffix reports whether the string s ends with suffix.
   466  func HasSuffix(s, suffix string) bool {
   467  	return stringslite.HasSuffix(s, suffix)
   468  }
   469  
   470  // Map returns a copy of the string s with all its characters modified
   471  // according to the mapping function. If mapping returns a negative value, the character is
   472  // dropped from the string with no replacement.
   473  func Map(mapping func(rune) rune, s string) string {
   474  	// In the worst case, the string can grow when mapped, making
   475  	// things unpleasant. But it's so rare we barge in assuming it's
   476  	// fine. It could also shrink but that falls out naturally.
   477  
   478  	// The output buffer b is initialized on demand, the first
   479  	// time a character differs.
   480  	var b Builder
   481  
   482  	for i, c := range s {
   483  		r := mapping(c)
   484  		if r == c && c != utf8.RuneError {
   485  			continue
   486  		}
   487  
   488  		var width int
   489  		if c == utf8.RuneError {
   490  			c, width = utf8.DecodeRuneInString(s[i:])
   491  			if width != 1 && r == c {
   492  				continue
   493  			}
   494  		} else {
   495  			width = utf8.RuneLen(c)
   496  		}
   497  
   498  		b.Grow(len(s) + utf8.UTFMax)
   499  		b.WriteString(s[:i])
   500  		if r >= 0 {
   501  			b.WriteRune(r)
   502  		}
   503  
   504  		s = s[i+width:]
   505  		break
   506  	}
   507  
   508  	// Fast path for unchanged input
   509  	if b.Cap() == 0 { // didn't call b.Grow above
   510  		return s
   511  	}
   512  
   513  	for _, c := range s {
   514  		r := mapping(c)
   515  
   516  		if r >= 0 {
   517  			// common case
   518  			// Due to inlining, it is more performant to determine if WriteByte should be
   519  			// invoked rather than always call WriteRune
   520  			if r < utf8.RuneSelf {
   521  				b.WriteByte(byte(r))
   522  			} else {
   523  				// r is not an ASCII rune.
   524  				b.WriteRune(r)
   525  			}
   526  		}
   527  	}
   528  
   529  	return b.String()
   530  }
   531  
   532  // According to static analysis, spaces, dashes, zeros, equals, and tabs
   533  // are the most commonly repeated string literal,
   534  // often used for display on fixed-width terminal windows.
   535  // Pre-declare constants for these for O(1) repetition in the common-case.
   536  const (
   537  	repeatedSpaces = "" +
   538  		"                                                                " +
   539  		"                                                                "
   540  	repeatedDashes = "" +
   541  		"----------------------------------------------------------------" +
   542  		"----------------------------------------------------------------"
   543  	repeatedZeroes = "" +
   544  		"0000000000000000000000000000000000000000000000000000000000000000"
   545  	repeatedEquals = "" +
   546  		"================================================================" +
   547  		"================================================================"
   548  	repeatedTabs = "" +
   549  		"\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t" +
   550  		"\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t"
   551  )
   552  
   553  // Repeat returns a new string consisting of count copies of the string s.
   554  //
   555  // It panics if count is negative or if the result of (len(s) * count)
   556  // overflows.
   557  func Repeat(s string, count int) string {
   558  	switch count {
   559  	case 0:
   560  		return ""
   561  	case 1:
   562  		return s
   563  	}
   564  
   565  	// Since we cannot return an error on overflow,
   566  	// we should panic if the repeat will generate an overflow.
   567  	// See golang.org/issue/16237.
   568  	if count < 0 {
   569  		panic("strings: negative Repeat count")
   570  	}
   571  	if len(s) > maxInt/count {
   572  		panic("strings: Repeat output length overflow")
   573  	}
   574  	n := len(s) * count
   575  
   576  	if len(s) == 0 {
   577  		return ""
   578  	}
   579  
   580  	// Optimize for commonly repeated strings of relatively short length.
   581  	switch s[0] {
   582  	case ' ', '-', '0', '=', '\t':
   583  		switch {
   584  		case n <= len(repeatedSpaces) && HasPrefix(repeatedSpaces, s):
   585  			return repeatedSpaces[:n]
   586  		case n <= len(repeatedDashes) && HasPrefix(repeatedDashes, s):
   587  			return repeatedDashes[:n]
   588  		case n <= len(repeatedZeroes) && HasPrefix(repeatedZeroes, s):
   589  			return repeatedZeroes[:n]
   590  		case n <= len(repeatedEquals) && HasPrefix(repeatedEquals, s):
   591  			return repeatedEquals[:n]
   592  		case n <= len(repeatedTabs) && HasPrefix(repeatedTabs, s):
   593  			return repeatedTabs[:n]
   594  		}
   595  	}
   596  
   597  	// Past a certain chunk size it is counterproductive to use
   598  	// larger chunks as the source of the write, as when the source
   599  	// is too large we are basically just thrashing the CPU D-cache.
   600  	// So if the result length is larger than an empirically-found
   601  	// limit (8KB), we stop growing the source string once the limit
   602  	// is reached and keep reusing the same source string - that
   603  	// should therefore be always resident in the L1 cache - until we
   604  	// have completed the construction of the result.
   605  	// This yields significant speedups (up to +100%) in cases where
   606  	// the result length is large (roughly, over L2 cache size).
   607  	const chunkLimit = 8 * 1024
   608  	chunkMax := n
   609  	if n > chunkLimit {
   610  		chunkMax = chunkLimit / len(s) * len(s)
   611  		if chunkMax == 0 {
   612  			chunkMax = len(s)
   613  		}
   614  	}
   615  
   616  	var b Builder
   617  	b.Grow(n)
   618  	b.WriteString(s)
   619  	for b.Len() < n {
   620  		chunk := n - b.Len()
   621  		if chunk > b.Len() {
   622  			chunk = b.Len()
   623  		}
   624  		if chunk > chunkMax {
   625  			chunk = chunkMax
   626  		}
   627  		b.WriteString(b.String()[:chunk])
   628  	}
   629  	return b.String()
   630  }
   631  
   632  // ToUpper returns s with all Unicode letters mapped to their upper case.
   633  func ToUpper(s string) string {
   634  	isASCII, hasLower := true, false
   635  	for i := 0; i < len(s); i++ {
   636  		c := s[i]
   637  		if c >= utf8.RuneSelf {
   638  			isASCII = false
   639  			break
   640  		}
   641  		hasLower = hasLower || ('a' <= c && c <= 'z')
   642  	}
   643  
   644  	if isASCII { // optimize for ASCII-only strings.
   645  		if !hasLower {
   646  			return s
   647  		}
   648  		var (
   649  			b   Builder
   650  			pos int
   651  		)
   652  		b.Grow(len(s))
   653  		for i := 0; i < len(s); i++ {
   654  			c := s[i]
   655  			if 'a' <= c && c <= 'z' {
   656  				c -= 'a' - 'A'
   657  				if pos < i {
   658  					b.WriteString(s[pos:i])
   659  				}
   660  				b.WriteByte(c)
   661  				pos = i + 1
   662  			}
   663  		}
   664  		if pos < len(s) {
   665  			b.WriteString(s[pos:])
   666  		}
   667  		return b.String()
   668  	}
   669  	return Map(unicode.ToUpper, s)
   670  }
   671  
   672  // ToLower returns s with all Unicode letters mapped to their lower case.
   673  func ToLower(s string) string {
   674  	isASCII, hasUpper := true, false
   675  	for i := 0; i < len(s); i++ {
   676  		c := s[i]
   677  		if c >= utf8.RuneSelf {
   678  			isASCII = false
   679  			break
   680  		}
   681  		hasUpper = hasUpper || ('A' <= c && c <= 'Z')
   682  	}
   683  
   684  	if isASCII { // optimize for ASCII-only strings.
   685  		if !hasUpper {
   686  			return s
   687  		}
   688  		var (
   689  			b   Builder
   690  			pos int
   691  		)
   692  		b.Grow(len(s))
   693  		for i := 0; i < len(s); i++ {
   694  			c := s[i]
   695  			if 'A' <= c && c <= 'Z' {
   696  				c += 'a' - 'A'
   697  				if pos < i {
   698  					b.WriteString(s[pos:i])
   699  				}
   700  				b.WriteByte(c)
   701  				pos = i + 1
   702  			}
   703  		}
   704  		if pos < len(s) {
   705  			b.WriteString(s[pos:])
   706  		}
   707  		return b.String()
   708  	}
   709  	return Map(unicode.ToLower, s)
   710  }
   711  
   712  // ToTitle returns a copy of the string s with all Unicode letters mapped to
   713  // their Unicode title case.
   714  func ToTitle(s string) string { return Map(unicode.ToTitle, s) }
   715  
   716  // ToUpperSpecial returns a copy of the string s with all Unicode letters mapped to their
   717  // upper case using the case mapping specified by c.
   718  func ToUpperSpecial(c unicode.SpecialCase, s string) string {
   719  	return Map(c.ToUpper, s)
   720  }
   721  
   722  // ToLowerSpecial returns a copy of the string s with all Unicode letters mapped to their
   723  // lower case using the case mapping specified by c.
   724  func ToLowerSpecial(c unicode.SpecialCase, s string) string {
   725  	return Map(c.ToLower, s)
   726  }
   727  
   728  // ToTitleSpecial returns a copy of the string s with all Unicode letters mapped to their
   729  // Unicode title case, giving priority to the special casing rules.
   730  func ToTitleSpecial(c unicode.SpecialCase, s string) string {
   731  	return Map(c.ToTitle, s)
   732  }
   733  
   734  // ToValidUTF8 returns a copy of the string s with each run of invalid UTF-8 byte sequences
   735  // replaced by the replacement string, which may be empty.
   736  func ToValidUTF8(s, replacement string) string {
   737  	var b Builder
   738  
   739  	for i, c := range s {
   740  		if c != utf8.RuneError {
   741  			continue
   742  		}
   743  
   744  		_, wid := utf8.DecodeRuneInString(s[i:])
   745  		if wid == 1 {
   746  			b.Grow(len(s) + len(replacement))
   747  			b.WriteString(s[:i])
   748  			s = s[i:]
   749  			break
   750  		}
   751  	}
   752  
   753  	// Fast path for unchanged input
   754  	if b.Cap() == 0 { // didn't call b.Grow above
   755  		return s
   756  	}
   757  
   758  	invalid := false // previous byte was from an invalid UTF-8 sequence
   759  	for i := 0; i < len(s); {
   760  		c := s[i]
   761  		if c < utf8.RuneSelf {
   762  			i++
   763  			invalid = false
   764  			b.WriteByte(c)
   765  			continue
   766  		}
   767  		_, wid := utf8.DecodeRuneInString(s[i:])
   768  		if wid == 1 {
   769  			i++
   770  			if !invalid {
   771  				invalid = true
   772  				b.WriteString(replacement)
   773  			}
   774  			continue
   775  		}
   776  		invalid = false
   777  		b.WriteString(s[i : i+wid])
   778  		i += wid
   779  	}
   780  
   781  	return b.String()
   782  }
   783  
   784  // isSeparator reports whether the rune could mark a word boundary.
   785  // TODO: update when package unicode captures more of the properties.
   786  func isSeparator(r rune) bool {
   787  	// ASCII alphanumerics and underscore are not separators
   788  	if r <= 0x7F {
   789  		switch {
   790  		case '0' <= r && r <= '9':
   791  			return false
   792  		case 'a' <= r && r <= 'z':
   793  			return false
   794  		case 'A' <= r && r <= 'Z':
   795  			return false
   796  		case r == '_':
   797  			return false
   798  		}
   799  		return true
   800  	}
   801  	// Letters and digits are not separators
   802  	if unicode.IsLetter(r) || unicode.IsDigit(r) {
   803  		return false
   804  	}
   805  	// Otherwise, all we can do for now is treat spaces as separators.
   806  	return unicode.IsSpace(r)
   807  }
   808  
   809  // Title returns a copy of the string s with all Unicode letters that begin words
   810  // mapped to their Unicode title case.
   811  //
   812  // Deprecated: The rule Title uses for word boundaries does not handle Unicode
   813  // punctuation properly. Use golang.org/x/text/cases instead.
   814  func Title(s string) string {
   815  	// Use a closure here to remember state.
   816  	// Hackish but effective. Depends on Map scanning in order and calling
   817  	// the closure once per rune.
   818  	prev := ' '
   819  	return Map(
   820  		func(r rune) rune {
   821  			if isSeparator(prev) {
   822  				prev = r
   823  				return unicode.ToTitle(r)
   824  			}
   825  			prev = r
   826  			return r
   827  		},
   828  		s)
   829  }
   830  
   831  // TrimLeftFunc returns a slice of the string s with all leading
   832  // Unicode code points c satisfying f(c) removed.
   833  func TrimLeftFunc(s string, f func(rune) bool) string {
   834  	i := indexFunc(s, f, false)
   835  	if i == -1 {
   836  		return ""
   837  	}
   838  	return s[i:]
   839  }
   840  
   841  // TrimRightFunc returns a slice of the string s with all trailing
   842  // Unicode code points c satisfying f(c) removed.
   843  func TrimRightFunc(s string, f func(rune) bool) string {
   844  	i := lastIndexFunc(s, f, false)
   845  	if i >= 0 && s[i] >= utf8.RuneSelf {
   846  		_, wid := utf8.DecodeRuneInString(s[i:])
   847  		i += wid
   848  	} else {
   849  		i++
   850  	}
   851  	return s[0:i]
   852  }
   853  
   854  // TrimFunc returns a slice of the string s with all leading
   855  // and trailing Unicode code points c satisfying f(c) removed.
   856  func TrimFunc(s string, f func(rune) bool) string {
   857  	return TrimRightFunc(TrimLeftFunc(s, f), f)
   858  }
   859  
   860  // IndexFunc returns the index into s of the first Unicode
   861  // code point satisfying f(c), or -1 if none do.
   862  func IndexFunc(s string, f func(rune) bool) int {
   863  	return indexFunc(s, f, true)
   864  }
   865  
   866  // LastIndexFunc returns the index into s of the last
   867  // Unicode code point satisfying f(c), or -1 if none do.
   868  func LastIndexFunc(s string, f func(rune) bool) int {
   869  	return lastIndexFunc(s, f, true)
   870  }
   871  
   872  // indexFunc is the same as IndexFunc except that if
   873  // truth==false, the sense of the predicate function is
   874  // inverted.
   875  func indexFunc(s string, f func(rune) bool, truth bool) int {
   876  	for i, r := range s {
   877  		if f(r) == truth {
   878  			return i
   879  		}
   880  	}
   881  	return -1
   882  }
   883  
   884  // lastIndexFunc is the same as LastIndexFunc except that if
   885  // truth==false, the sense of the predicate function is
   886  // inverted.
   887  func lastIndexFunc(s string, f func(rune) bool, truth bool) int {
   888  	for i := len(s); i > 0; {
   889  		r, size := utf8.DecodeLastRuneInString(s[0:i])
   890  		i -= size
   891  		if f(r) == truth {
   892  			return i
   893  		}
   894  	}
   895  	return -1
   896  }
   897  
   898  // asciiSet is a 32-byte value, where each bit represents the presence of a
   899  // given ASCII character in the set. The 128-bits of the lower 16 bytes,
   900  // starting with the least-significant bit of the lowest word to the
   901  // most-significant bit of the highest word, map to the full range of all
   902  // 128 ASCII characters. The 128-bits of the upper 16 bytes will be zeroed,
   903  // ensuring that any non-ASCII character will be reported as not in the set.
   904  // This allocates a total of 32 bytes even though the upper half
   905  // is unused to avoid bounds checks in asciiSet.contains.
   906  type asciiSet [8]uint32
   907  
   908  // makeASCIISet creates a set of ASCII characters and reports whether all
   909  // characters in chars are ASCII.
   910  func makeASCIISet(chars string) (as asciiSet, ok bool) {
   911  	for i := 0; i < len(chars); i++ {
   912  		c := chars[i]
   913  		if c >= utf8.RuneSelf {
   914  			return as, false
   915  		}
   916  		as[c/32] |= 1 << (c % 32)
   917  	}
   918  	return as, true
   919  }
   920  
   921  // contains reports whether c is inside the set.
   922  func (as *asciiSet) contains(c byte) bool {
   923  	return (as[c/32] & (1 << (c % 32))) != 0
   924  }
   925  
   926  // Trim returns a slice of the string s with all leading and
   927  // trailing Unicode code points contained in cutset removed.
   928  func Trim(s, cutset string) string {
   929  	if s == "" || cutset == "" {
   930  		return s
   931  	}
   932  	if len(cutset) == 1 && cutset[0] < utf8.RuneSelf {
   933  		return trimLeftByte(trimRightByte(s, cutset[0]), cutset[0])
   934  	}
   935  	if as, ok := makeASCIISet(cutset); ok {
   936  		return trimLeftASCII(trimRightASCII(s, &as), &as)
   937  	}
   938  	return trimLeftUnicode(trimRightUnicode(s, cutset), cutset)
   939  }
   940  
   941  // TrimLeft returns a slice of the string s with all leading
   942  // Unicode code points contained in cutset removed.
   943  //
   944  // To remove a prefix, use [TrimPrefix] instead.
   945  func TrimLeft(s, cutset string) string {
   946  	if s == "" || cutset == "" {
   947  		return s
   948  	}
   949  	if len(cutset) == 1 && cutset[0] < utf8.RuneSelf {
   950  		return trimLeftByte(s, cutset[0])
   951  	}
   952  	if as, ok := makeASCIISet(cutset); ok {
   953  		return trimLeftASCII(s, &as)
   954  	}
   955  	return trimLeftUnicode(s, cutset)
   956  }
   957  
   958  func trimLeftByte(s string, c byte) string {
   959  	for len(s) > 0 && s[0] == c {
   960  		s = s[1:]
   961  	}
   962  	return s
   963  }
   964  
   965  func trimLeftASCII(s string, as *asciiSet) string {
   966  	for len(s) > 0 {
   967  		if !as.contains(s[0]) {
   968  			break
   969  		}
   970  		s = s[1:]
   971  	}
   972  	return s
   973  }
   974  
   975  func trimLeftUnicode(s, cutset string) string {
   976  	for len(s) > 0 {
   977  		r, n := rune(s[0]), 1
   978  		if r >= utf8.RuneSelf {
   979  			r, n = utf8.DecodeRuneInString(s)
   980  		}
   981  		if !ContainsRune(cutset, r) {
   982  			break
   983  		}
   984  		s = s[n:]
   985  	}
   986  	return s
   987  }
   988  
   989  // TrimRight returns a slice of the string s, with all trailing
   990  // Unicode code points contained in cutset removed.
   991  //
   992  // To remove a suffix, use [TrimSuffix] instead.
   993  func TrimRight(s, cutset string) string {
   994  	if s == "" || cutset == "" {
   995  		return s
   996  	}
   997  	if len(cutset) == 1 && cutset[0] < utf8.RuneSelf {
   998  		return trimRightByte(s, cutset[0])
   999  	}
  1000  	if as, ok := makeASCIISet(cutset); ok {
  1001  		return trimRightASCII(s, &as)
  1002  	}
  1003  	return trimRightUnicode(s, cutset)
  1004  }
  1005  
  1006  func trimRightByte(s string, c byte) string {
  1007  	for len(s) > 0 && s[len(s)-1] == c {
  1008  		s = s[:len(s)-1]
  1009  	}
  1010  	return s
  1011  }
  1012  
  1013  func trimRightASCII(s string, as *asciiSet) string {
  1014  	for len(s) > 0 {
  1015  		if !as.contains(s[len(s)-1]) {
  1016  			break
  1017  		}
  1018  		s = s[:len(s)-1]
  1019  	}
  1020  	return s
  1021  }
  1022  
  1023  func trimRightUnicode(s, cutset string) string {
  1024  	for len(s) > 0 {
  1025  		r, n := rune(s[len(s)-1]), 1
  1026  		if r >= utf8.RuneSelf {
  1027  			r, n = utf8.DecodeLastRuneInString(s)
  1028  		}
  1029  		if !ContainsRune(cutset, r) {
  1030  			break
  1031  		}
  1032  		s = s[:len(s)-n]
  1033  	}
  1034  	return s
  1035  }
  1036  
  1037  // TrimSpace returns a slice of the string s, with all leading
  1038  // and trailing white space removed, as defined by Unicode.
  1039  func TrimSpace(s string) string {
  1040  	// Fast path for ASCII: look for the first ASCII non-space byte
  1041  	start := 0
  1042  	for ; start < len(s); start++ {
  1043  		c := s[start]
  1044  		if c >= utf8.RuneSelf {
  1045  			// If we run into a non-ASCII byte, fall back to the
  1046  			// slower unicode-aware method on the remaining bytes
  1047  			return TrimFunc(s[start:], unicode.IsSpace)
  1048  		}
  1049  		if asciiSpace[c] == 0 {
  1050  			break
  1051  		}
  1052  	}
  1053  
  1054  	// Now look for the first ASCII non-space byte from the end
  1055  	stop := len(s)
  1056  	for ; stop > start; stop-- {
  1057  		c := s[stop-1]
  1058  		if c >= utf8.RuneSelf {
  1059  			// start has been already trimmed above, should trim end only
  1060  			return TrimRightFunc(s[start:stop], unicode.IsSpace)
  1061  		}
  1062  		if asciiSpace[c] == 0 {
  1063  			break
  1064  		}
  1065  	}
  1066  
  1067  	// At this point s[start:stop] starts and ends with an ASCII
  1068  	// non-space bytes, so we're done. Non-ASCII cases have already
  1069  	// been handled above.
  1070  	return s[start:stop]
  1071  }
  1072  
  1073  // TrimPrefix returns s without the provided leading prefix string.
  1074  // If s doesn't start with prefix, s is returned unchanged.
  1075  func TrimPrefix(s, prefix string) string {
  1076  	return stringslite.TrimPrefix(s, prefix)
  1077  }
  1078  
  1079  // TrimSuffix returns s without the provided trailing suffix string.
  1080  // If s doesn't end with suffix, s is returned unchanged.
  1081  func TrimSuffix(s, suffix string) string {
  1082  	return stringslite.TrimSuffix(s, suffix)
  1083  }
  1084  
  1085  // Replace returns a copy of the string s with the first n
  1086  // non-overlapping instances of old replaced by new.
  1087  // If old is empty, it matches at the beginning of the string
  1088  // and after each UTF-8 sequence, yielding up to k+1 replacements
  1089  // for a k-rune string.
  1090  // If n < 0, there is no limit on the number of replacements.
  1091  func Replace(s, old, new string, n int) string {
  1092  	if old == new || n == 0 {
  1093  		return s // avoid allocation
  1094  	}
  1095  
  1096  	// Compute number of replacements.
  1097  	if m := Count(s, old); m == 0 {
  1098  		return s // avoid allocation
  1099  	} else if n < 0 || m < n {
  1100  		n = m
  1101  	}
  1102  
  1103  	// Apply replacements to buffer.
  1104  	var b Builder
  1105  	b.Grow(len(s) + n*(len(new)-len(old)))
  1106  	start := 0
  1107  	for i := 0; i < n; i++ {
  1108  		j := start
  1109  		if len(old) == 0 {
  1110  			if i > 0 {
  1111  				_, wid := utf8.DecodeRuneInString(s[start:])
  1112  				j += wid
  1113  			}
  1114  		} else {
  1115  			j += Index(s[start:], old)
  1116  		}
  1117  		b.WriteString(s[start:j])
  1118  		b.WriteString(new)
  1119  		start = j + len(old)
  1120  	}
  1121  	b.WriteString(s[start:])
  1122  	return b.String()
  1123  }
  1124  
  1125  // ReplaceAll returns a copy of the string s with all
  1126  // non-overlapping instances of old replaced by new.
  1127  // If old is empty, it matches at the beginning of the string
  1128  // and after each UTF-8 sequence, yielding up to k+1 replacements
  1129  // for a k-rune string.
  1130  func ReplaceAll(s, old, new string) string {
  1131  	return Replace(s, old, new, -1)
  1132  }
  1133  
  1134  // EqualFold reports whether s and t, interpreted as UTF-8 strings,
  1135  // are equal under simple Unicode case-folding, which is a more general
  1136  // form of case-insensitivity.
  1137  func EqualFold(s, t string) bool {
  1138  	// ASCII fast path
  1139  	i := 0
  1140  	for ; i < len(s) && i < len(t); i++ {
  1141  		sr := s[i]
  1142  		tr := t[i]
  1143  		if sr|tr >= utf8.RuneSelf {
  1144  			goto hasUnicode
  1145  		}
  1146  
  1147  		// Easy case.
  1148  		if tr == sr {
  1149  			continue
  1150  		}
  1151  
  1152  		// Make sr < tr to simplify what follows.
  1153  		if tr < sr {
  1154  			tr, sr = sr, tr
  1155  		}
  1156  		// ASCII only, sr/tr must be upper/lower case
  1157  		if 'A' <= sr && sr <= 'Z' && tr == sr+'a'-'A' {
  1158  			continue
  1159  		}
  1160  		return false
  1161  	}
  1162  	// Check if we've exhausted both strings.
  1163  	return len(s) == len(t)
  1164  
  1165  hasUnicode:
  1166  	s = s[i:]
  1167  	t = t[i:]
  1168  	for _, sr := range s {
  1169  		// If t is exhausted the strings are not equal.
  1170  		if len(t) == 0 {
  1171  			return false
  1172  		}
  1173  
  1174  		// Extract first rune from second string.
  1175  		var tr rune
  1176  		if t[0] < utf8.RuneSelf {
  1177  			tr, t = rune(t[0]), t[1:]
  1178  		} else {
  1179  			r, size := utf8.DecodeRuneInString(t)
  1180  			tr, t = r, t[size:]
  1181  		}
  1182  
  1183  		// If they match, keep going; if not, return false.
  1184  
  1185  		// Easy case.
  1186  		if tr == sr {
  1187  			continue
  1188  		}
  1189  
  1190  		// Make sr < tr to simplify what follows.
  1191  		if tr < sr {
  1192  			tr, sr = sr, tr
  1193  		}
  1194  		// Fast check for ASCII.
  1195  		if tr < utf8.RuneSelf {
  1196  			// ASCII only, sr/tr must be upper/lower case
  1197  			if 'A' <= sr && sr <= 'Z' && tr == sr+'a'-'A' {
  1198  				continue
  1199  			}
  1200  			return false
  1201  		}
  1202  
  1203  		// General case. SimpleFold(x) returns the next equivalent rune > x
  1204  		// or wraps around to smaller values.
  1205  		r := unicode.SimpleFold(sr)
  1206  		for r != sr && r < tr {
  1207  			r = unicode.SimpleFold(r)
  1208  		}
  1209  		if r == tr {
  1210  			continue
  1211  		}
  1212  		return false
  1213  	}
  1214  
  1215  	// First string is empty, so check if the second one is also empty.
  1216  	return len(t) == 0
  1217  }
  1218  
  1219  // Index returns the index of the first instance of substr in s, or -1 if substr is not present in s.
  1220  func Index(s, substr string) int {
  1221  	return stringslite.Index(s, substr)
  1222  }
  1223  
  1224  // Cut slices s around the first instance of sep,
  1225  // returning the text before and after sep.
  1226  // The found result reports whether sep appears in s.
  1227  // If sep does not appear in s, cut returns s, "", false.
  1228  func Cut(s, sep string) (before, after string, found bool) {
  1229  	return stringslite.Cut(s, sep)
  1230  }
  1231  
  1232  // CutPrefix returns s without the provided leading prefix string
  1233  // and reports whether it found the prefix.
  1234  // If s doesn't start with prefix, CutPrefix returns s, false.
  1235  // If prefix is the empty string, CutPrefix returns s, true.
  1236  func CutPrefix(s, prefix string) (after string, found bool) {
  1237  	return stringslite.CutPrefix(s, prefix)
  1238  }
  1239  
  1240  // CutSuffix returns s without the provided ending suffix string
  1241  // and reports whether it found the suffix.
  1242  // If s doesn't end with suffix, CutSuffix returns s, false.
  1243  // If suffix is the empty string, CutSuffix returns s, true.
  1244  func CutSuffix(s, suffix string) (before string, found bool) {
  1245  	return stringslite.CutSuffix(s, suffix)
  1246  }
  1247  

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