[stdlib] Slice._bounds, Range<String.Index>._encodedOffsetRange: New helpers

Author: lorentey

stdlib/public/core/Range.swift

@@ -1027,3 +1027,14 @@ extension PartialRangeUpTo: Sendable where Bound: Sendable { }
 extension PartialRangeThrough: Sendable where Bound: Sendable { }
 extension PartialRangeFrom: Sendable where Bound: Sendable { }
 extension PartialRangeFrom.Iterator: Sendable where Bound: Sendable { }
+
+extension Range where Bound == String.Index {
+  @_alwaysEmitIntoClient // Swift 5.7
+  internal var _encodedOffsetRange: Range<Int> {
+    _internalInvariant(
+      (lowerBound._canBeUTF8 && upperBound._canBeUTF8)
+      || (lowerBound._canBeUTF16 && upperBound._canBeUTF16))
+    return Range<Int>(
+      _uncheckedBounds: (lowerBound._encodedOffset, upperBound._encodedOffset))
+  }
+}

stdlib/public/core/Slice.swift

@@ -135,6 +135,11 @@ public struct Slice<Base: Collection> {
   public var base: Base {
     return _base
   }
+
+  @_alwaysEmitIntoClient @inline(__always)
+  internal var _bounds: Range<Base.Index> {
+    Range(_uncheckedBounds: (_startIndex, _endIndex))
+  }
 }
 
 extension Slice: Collection {
@@ -157,21 +162,21 @@ extension Slice: Collection {
   @inlinable // generic-performance
   public subscript(index: Index) -> Base.Element {
     get {
-      _failEarlyRangeCheck(index, bounds: startIndex..<endIndex)
+      _failEarlyRangeCheck(index, bounds: _bounds)
       return _base[index]
     }
   }
 
   @inlinable // generic-performance
   public subscript(bounds: Range<Index>) -> Slice<Base> {
     get {
-      _failEarlyRangeCheck(bounds, bounds: startIndex..<endIndex)
+      _failEarlyRangeCheck(bounds, bounds: _bounds)
       return Slice(base: _base, bounds: bounds)
     }
   }
 
-  public var indices: Indices { 
-    return _base.indices[_startIndex..<_endIndex]
+  public var indices: Indices {
+    return _base.indices[_bounds]
   }
 
   @inlinable // generic-performance
@@ -264,11 +269,11 @@ extension Slice: MutableCollection where Base: MutableCollection {
   @inlinable // generic-performance
   public subscript(index: Index) -> Base.Element {
     get {
-      _failEarlyRangeCheck(index, bounds: startIndex..<endIndex)
+      _failEarlyRangeCheck(index, bounds: _bounds)
       return _base[index]
     }
     set {
-      _failEarlyRangeCheck(index, bounds: startIndex..<endIndex)
+      _failEarlyRangeCheck(index, bounds: _bounds)
       _base[index] = newValue
       // MutableSlice requires that the underlying collection's subscript
       // setter does not invalidate indices, so our `startIndex` and `endIndex`
@@ -279,7 +284,7 @@ extension Slice: MutableCollection where Base: MutableCollection {
   @inlinable // generic-performance
   public subscript(bounds: Range<Index>) -> Slice<Base> {
     get {
-      _failEarlyRangeCheck(bounds, bounds: startIndex..<endIndex)
+      _failEarlyRangeCheck(bounds, bounds: _bounds)
       return Slice(base: _base, bounds: bounds)
     }
     set {

stdlib/public/core/Substring.swift

@@ -113,9 +113,8 @@ public struct Substring: Sendable {
   @usableFromInline // This used to be @inlinable before 5.7
   @available(*, deprecated) // Use `init(_unchecked:)` in new code.
   internal init(_ slice: Slice<String>) {
-    let r = slice.base._guts.validateScalarRange(
-      slice.startIndex ..< slice.endIndex)
-    self._slice = Slice(base: slice.base, bounds: r)
+    let r = slice._base._guts.validateScalarRange(slice._bounds)
+    self._slice = Slice(base: slice._base, bounds: r)
     _invariantCheck()
   }
 
@@ -137,19 +136,13 @@ extension Substring {
   public var base: String { return _slice._base }
 
   @inlinable @inline(__always)
-  internal var _wholeGuts: _StringGuts { return _slice._base._guts }
+  internal var _wholeGuts: _StringGuts { _slice._base._guts }
 
   @inlinable @inline(__always)
-  internal var _offsetRange: Range<Int> {
-    let lower = _slice._startIndex._encodedOffset
-    let upper = _slice._endIndex._encodedOffset
-    return Range(_uncheckedBounds: (lower, upper))
-  }
+  internal var _offsetRange: Range<Int> { _slice._bounds._encodedOffsetRange }
 
   @inlinable @inline(__always)
-  internal var _bounds: Range<Index> {
-    Range(_uncheckedBounds: (startIndex, endIndex))
-  }
+  internal var _bounds: Range<Index> { _slice._bounds }
 }
 
 extension Substring {
@@ -746,9 +739,7 @@ extension Substring {
     internal var _base: String.UTF8View { _slice._base }
 
     @_alwaysEmitIntoClient @inline(__always)
-    internal var _bounds: Range<Index> {
-      Range(_uncheckedBounds: (_slice._startIndex, _slice._endIndex))
-    }
+    internal var _bounds: Range<Index> { _slice._bounds }
   }
 }
 
@@ -912,9 +903,7 @@ extension Substring {
     internal var _base: String.UTF16View { _slice._base }
 
     @_alwaysEmitIntoClient @inline(__always)
-    internal var _bounds: Range<Index> {
-      Range(_uncheckedBounds: (_slice._startIndex, _slice._endIndex))
-    }
+    internal var _bounds: Range<Index> { _slice._bounds }
   }
 }
 
@@ -1075,21 +1064,15 @@ extension Substring {
 }
 
 extension Substring.UnicodeScalarView {
-  @_alwaysEmitIntoClient
-  @inline(__always)
+  @_alwaysEmitIntoClient @inline(__always)
   internal var _wholeGuts: _StringGuts { _slice._base._guts }
 
   @inline(__always)
-  internal var _offsetRange: Range<Int> {
-    let lower = _slice._startIndex._encodedOffset
-    let upper = _slice._endIndex._encodedOffset
-    return Range(_uncheckedBounds: (lower, upper))
-  }
+  internal var _offsetRange: Range<Int> { _slice._bounds._encodedOffsetRange }
 
   @_alwaysEmitIntoClient
   @inline(__always)
-  internal var _bounds: Range<Index> {
-    Range(_uncheckedBounds: (startIndex, endIndex))
+  internal var _bounds: Range<Index> { _slice._bounds }
   }
 }