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[stdlib] Fix string index sharing (#4896)

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* [stdlib] Fix String.UTF16View index sharing

* [stdlib] Fix String.UnicodeScalarView index sharing

* [stdlib] Fix String.CharacterView index sharing

* [stdlib] Test advancing string indices past their ends

* [stdlib] Simplify CharacterView ranged subscript
This commit is contained in:
Nate Cook
2016-10-13 12:19:38 -05:00
committed by Maxim Moiseev
parent 91bba4d425
commit c2bc72d9d6
4 changed files with 93 additions and 55 deletions
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34
stdlib/public/core/StringUTF16.swift
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@@ -145,7 +145,7 @@ extension String {
/// The position of the first code unit if the `String` is
/// nonempty; identical to `endIndex` otherwise.
public var startIndex: Index {
return Index(_offset: 0)
return Index(_offset: _offset)
}
/// The "past the end" position---that is, the position one greater than
@@ -153,7 +153,7 @@ extension String {
///
/// In an empty UTF-16 view, `endIndex` is equal to `startIndex`.
public var endIndex: Index {
return Index(_offset: _length)
return Index(_offset: _offset + _length)
}
public struct Indices {
@@ -204,7 +204,7 @@ extension String {
}
func _internalIndex(at i: Int) -> Int {
return _core.startIndex + _offset + i
return _core.startIndex + i
}
/// Accesses the code unit at the given position.
@@ -220,11 +220,10 @@ extension String {
/// - Parameter position: A valid index of the view. `position` must be
/// less than the view's end index.
public subscript(i: Index) -> UTF16.CodeUnit {
let position = i._offset
_precondition(position >= 0 && position < _length,
_precondition(i >= startIndex && i < endIndex,
"out-of-range access on a UTF16View")
let index = _internalIndex(at: position)
let index = _internalIndex(at: i._offset)
let u = _core[index]
if _fastPath((u >> 11) != 0b1101_1) {
// Neither high-surrogate, nor low-surrogate -- well-formed sequence
@@ -292,8 +291,8 @@ extension String {
}
public var description: String {
let start = _internalIndex(at: 0)
let end = _internalIndex(at: _length)
let start = _internalIndex(at: _offset)
let end = _internalIndex(at: _offset + _length)
return String(_core[start..<end])
}
@@ -337,17 +336,16 @@ extension String {
public init?(_ utf16: UTF16View) {
let wholeString = String(utf16._core)
if let start = UTF16Index(
_offset: utf16._offset
).samePosition(in: wholeString) {
if let end = UTF16Index(
_offset: utf16._offset + utf16._length
).samePosition(in: wholeString) {
self = wholeString[start..<end]
return
}
guard
let start = UTF16Index(_offset: utf16._offset)
.samePosition(in: wholeString),
let end = UTF16Index(_offset: utf16._offset + utf16._length)
.samePosition(in: wholeString)
else
{
return nil
}
return nil
self = wholeString[start..<end]
}
/// The index type for subscripting a string's `utf16` view.