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[stdlib] Factor scalar-aligned String index validation out into a set of common routines

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There are three flavors, corresponding to i < endIndex, i <= endIndex, and range containment checks.
Additionally, we have separate variants for index validation in substrings.
This commit is contained in:
Karoy Lorentey
2022-03-01 23:27:40 -08:00
parent 15c7721caf
commit a44997eeea
6 changed files with 337 additions and 127 deletions
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8
stdlib/public/core/StringUnicodeScalarView.swift
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@@ -108,6 +108,7 @@ extension String.UnicodeScalarView: BidirectionalCollection {
public func index(after i: Index) -> Index {
// TODO(String performance): isASCII fast-path
// TODO(lorentey): Review index validation
_precondition(i < endIndex, "String index is out of bounds")
let i = _guts.scalarAlign(i)
@@ -121,6 +122,7 @@ extension String.UnicodeScalarView: BidirectionalCollection {
@_alwaysEmitIntoClient // Swift 5.1 bug fix
public func distance(from start: Index, to end: Index) -> Int {
// TODO(lorentey): Review index validation
return _distance(from: _guts.scalarAlign(start), to: _guts.scalarAlign(end))
}
@@ -129,6 +131,7 @@ extension String.UnicodeScalarView: BidirectionalCollection {
/// - Precondition: The previous location exists.
@inlinable @inline(__always)
public func index(before i: Index) -> Index {
// TODO(lorentey): Review index validation
// TODO(String performance): isASCII fast-path
// Note: bounds checking in `index(before:)` is tricky as scalar aligning an
@@ -168,6 +171,7 @@ extension String.UnicodeScalarView: BidirectionalCollection {
/// must be less than the view's end index.
@inlinable @inline(__always)
public subscript(position: Index) -> Unicode.Scalar {
// TODO(lorentey): Review index validation
String(_guts)._boundsCheck(position)
let i = _guts.scalarAlign(position)
return _guts.errorCorrectedScalar(startingAt: i._encodedOffset).0
@@ -314,6 +318,7 @@ extension String.UnicodeScalarView: RangeReplaceableCollection {
_ bounds: Range<Index>,
with newElements: C
) where C: Collection, C.Element == Unicode.Scalar {
// TODO(lorentey): Review index validation
// TODO(String performance): Skip extra String and Array allocation
let utf8Replacement = newElements.flatMap { String($0).utf8 }
@@ -358,6 +363,7 @@ extension String.UnicodeScalarIndex {
_ sourcePosition: String.Index,
within unicodeScalars: String.UnicodeScalarView
) {
// TODO(lorentey): Review index validation
guard unicodeScalars._guts.isOnUnicodeScalarBoundary(sourcePosition) else {
return nil
}
@@ -385,6 +391,7 @@ extension String.UnicodeScalarIndex {
/// an attempt to convert the position of a UTF-8 continuation byte
/// returns `nil`.
public func samePosition(in characters: String) -> String.Index? {
// TODO(lorentey): Review index validation
return String.Index(self, within: characters)
}
}
@@ -414,6 +421,7 @@ extension String.UnicodeScalarView {
@available(swift, introduced: 4)
public subscript(r: Range<Index>) -> String.UnicodeScalarView.SubSequence {
// TODO(lorentey): Review index validation
_failEarlyRangeCheck(r, bounds: startIndex..<endIndex)
return String.UnicodeScalarView.SubSequence(self, _bounds: r)
}