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[stdlib] String index interchange, part II (UTF16)

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This commit is contained in:
Dave Abrahams
2017-05-20 15:01:38 -07:00
parent e523c80339
commit 2e0bb2f533
13 changed files with 78 additions and 268 deletions
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38
stdlib/public/core/StringUnicodeScalarView.swift
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@@ -433,7 +433,7 @@ extension String.UnicodeScalarIndex {
return nil
}
}
self.init(encodedOffset: utf16Index._offset)
self = utf16Index
}
/// Creates an index in the given Unicode scalars view that corresponds
@@ -466,31 +466,6 @@ extension String.UnicodeScalarIndex {
self.init(encodedOffset: utf8Index._coreIndex)
}
/// Creates an index in the given Unicode scalars view that corresponds
/// exactly to the specified string position.
///
/// The following example converts the position of the teacup emoji (`"🍵"`)
/// into its corresponding position in the string's `unicodeScalars` view.
///
/// let cafe = "Café 🍵"
/// let stringIndex = cafe.index(of: "🍵")!
/// let scalarIndex = String.UnicodeScalarView.Index(stringIndex, within: cafe.unicodeScalars)
///
/// print(cafe.unicodeScalars[scalarIndex...])
/// // Prints "🍵"
///
/// - Parameters:
/// - index: A position in a string. `index` must be an element of
/// `String(unicodeScalars).indices`.
/// - unicodeScalars: The `UnicodeScalarView` in which to find the new
/// position.
public init(
_ index: String.Index,
within unicodeScalars: String.UnicodeScalarView
) {
self.init(encodedOffset: index.encodedOffset)
}
/// Returns the position in the given string that corresponds exactly to this
/// index.
///
@@ -518,9 +493,20 @@ extension String.UnicodeScalarIndex {
}
extension String.UnicodeScalarView {
internal func _isOnUnicodeScalarBoundary(_ i: Index) -> Bool {
if _fastPath(_core.isASCII) { return true }
if i == startIndex || i == endIndex {
return true
}
let i2 = _toCoreIndex(i)
if _fastPath(_core[i2] & 0xFC00 != 0xDC00) { return true }
return _core[i2 &- 1] & 0xFC00 != 0xD800
}
// NOTE: Don't make this function inlineable. Grapheme cluster
// segmentation uses a completely different algorithm in Unicode 9.0.
internal func _isOnGraphemeClusterBoundary(_ i: Index) -> Bool {
if !_isOnUnicodeScalarBoundary(i) { return false }
if i == startIndex || i == endIndex {
return true
}