code review 824043: Unicode: provide an ability to supplement the case-mapp...

src/pkg/unicode/letter.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.
 
 // This package provides data and functions to test some properties of Unicode code points.
 package unicode
 
 const (
         MaxRune         = 0x10FFFF // Maximum valid Unicode code point.
         ReplacementChar = 0xFFFD   // Represents invalid code points.
 )
 
 
 // The representation of a range of Unicode code points.  The range runs from Lo to Hi
 // inclusive and has the specified stride.
 type Range struct {
         Lo     int
         Hi     int
         Stride int
 }
 
-// The representation of a range of Unicode code points for case conversion.
+// CaseRange represents a range of Unicode code points for simple (one
+// code point to one code point) case conversion.
 // The range runs from Lo to Hi inclusive, with a fixed stride of 1.  Deltas
 // are the number to add to the code point to reach the code point for a
 // different case for that character.  They may be negative.  If zero, it
 // means the character is in the corresponding case. There is a special
 // case representing sequences of alternating corresponding Upper and Lower
 // pairs.  It appears with a fixed Delta of
 //      {UpperLower, UpperLower, UpperLower}
 // The constant UpperLower has an otherwise impossible delta value.
+// TODO: Provide a mechanism for full case folding (those that involve

[rsc1, 2010/03/31 00:39:31]

If you move this out of the doc comment you can say

// BUG(r): There should be a mechanism for full case folding
// (those that involve multiple runes in the input or output).

at top level as its own comment, and it appears in the
BUGS section of the godoc output.

+// multiple runes in the input or output).
 type CaseRange struct {
         Lo    int
         Hi    int
         Delta d
 }
 
+// SpecialCase represents language-specific case mappings such as Turkish.
+// TODO: Provide a mechanism for full case folding (those that involve

[rsc1, 2010/03/31 00:39:31]

Then you can drop this one.
(But keep Methods of SpecialCase...)

+// multiple runes in the input or output).  Methods of SpecialCase
+// customize (by overriding) the standard mappings.
+type SpecialCase []CaseRange
+
 // Indices into the Delta arrays inside CaseRanges for case mapping.
 const (
         UpperCase = iota
         LowerCase
         TitleCase
         MaxCase
 )
 
 type d [MaxCase]int32 // to make the CaseRanges text shorter
 
@@ skipping 76 matching lines @@
         if rune <= 0xFF { // quick Latin-1 check
                 switch rune {
                 case '\t', '\n', '\v', '\f', '\r', ' ', 0x85, 0xA0:
                         return true
                 }
                 return false
         }
         return Is(White_Space, rune)
 }
 
-// To maps the rune to the specified case: UpperCase, LowerCase, or TitleCase.
-func To(_case int, rune int) int {
+// to maps the rune using the specified case mapping.
+func to(_case int, rune int, caseRange []CaseRange) int {
         if _case < 0 || MaxCase <= _case {
                 return ReplacementChar // as reasonable an error as any
         }
         // binary search over ranges
         lo := 0
-        hi := len(CaseRanges)
+        hi := len(caseRange)
         for lo < hi {
                 m := lo + (hi-lo)/2
-                r := CaseRanges[m]
+                r := caseRange[m]
                 if r.Lo <= rune && rune <= r.Hi {
                         delta := int(r.Delta[_case])
                         if delta > MaxRune {
                                 // In an Upper-Lower sequence, which always starts with
                                 // an UpperCase letter, the real deltas always look like:
                                 //      {0, 1, 0}    UpperCase (Lower is next)
                                 //      {-1, 0, -1}  LowerCase (Upper, Title are previous)
                                 // The characters at even offsets from the beginning of the
                                 // sequence are upper case; the ones at odd offsets are lower.
                                 // The correct mapping can be done by clearing or setting the low
                                 // bit in the sequence offset.
                                 // The constants UpperCase and TitleCase are even while LowerCase
                                 // is odd so we take the low bit from _case.
                                 return r.Lo + ((rune-r.Lo)&^1 | _case&1)
                         }
                         return rune + delta
                 }
                 if rune < r.Lo {
                         hi = m
                 } else {
                         lo = m + 1
                 }
         }
         return rune
 }
 
+// To maps the rune to the specified case: UpperCase, LowerCase, or TitleCase.
+func To(_case int, rune int) int {
+        return to(_case, rune, CaseRanges)
+}
+
 // ToUpper maps the rune to upper case.
 func ToUpper(rune int) int {
         if rune < 0x80 { // quick ASCII check
                 if 'a' <= rune && rune <= 'z' {
                         rune -= 'a' - 'A'
                 }
                 return rune
         }
         return To(UpperCase, rune)
 }
@@ skipping 12 matching lines @@
 // ToTitle maps the rune to title case.
 func ToTitle(rune int) int {
         if rune < 0x80 { // quick ASCII check
                 if 'a' <= rune && rune <= 'z' { // title case is upper case for ASCII
                         rune -= 'a' - 'A'
                 }
                 return rune
         }
         return To(TitleCase, rune)
 }
+
+// ToUpper maps the rune to upper case giving priority to the special mapping.
+func (special SpecialCase) ToUpper(rune int) int {
+        r := to(UpperCase, rune, []CaseRange(special))
+        if r == rune {
+                r = ToUpper(rune)
+        }
+        return r
+}
+
+// ToTitlemaps the rune to upper case giving priority to the special mapping.
+func (special SpecialCase) ToTitle(rune int) int {
+        r := to(TitleCase, rune, []CaseRange(special))
+        if r == rune {
+                r = ToTitle(rune)
+        }
+        return r
+}
+
+// ToLower maps the rune to upper case giving priority to the special mapping.
+func (special SpecialCase) ToLower(rune int) int {
+        r := to(LowerCase, rune, []CaseRange(special))
+        if r == rune {
+                r = ToLower(rune)
+        }
+        return r
+}