Remove refs to Countable ranges

Azoy · Feb 3, 2018 · e61e1f5 · e61e1f5
1 parent 4f4f65e
commit e61e1f5
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Showing 4 changed files with 103 additions and 2 deletions.
diff --git a/stdlib/public/core/ClosedRange.swift b/stdlib/public/core/ClosedRange.swift
@@ -459,6 +459,57 @@ extension ClosedRange where Bound: Strideable, Bound.Stride : SignedInteger {
   }
 }
 
+extension ClosedRange
+where Bound : FixedWidthInteger,
+      Bound.Magnitude : UnsignedInteger {
+
+  /// Returns a random element from this collection.
+  ///
+  /// - Parameter generator: The random number generator to use when getting
+  ///   a random element.
+  /// - Returns: A random element from this collection.
+  ///
+  /// A good example of this is getting a random greeting from an array:
+  ///
+  ///     let greetings = ["hi", "hey", "hello", "hola"]
+  ///     let randomGreeting = greetings.random()
+  ///
+  /// If the collection is empty, the value of this function is `nil`.
+  ///
+  ///     let numbers = [10, 20, 30, 40, 50]
+  ///     if let randomNumber = numbers.random() {
+  ///         print(randomNumber)
+  ///     }
+  ///     // Could print "20", perhaps
+  @_inlineable
+  public func random(
+    using generator: RandomNumberGenerator = Random.default
+  ) -> Element? {
+    let isLowerNegative = Bound.isSigned && lowerBound < 0
+    let sameSign = !Bound.isSigned || isLowerNegative == (upperBound < 0)
+    var delta: Bound.Magnitude
+    if isLowerNegative {
+      delta = sameSign
+        ? lowerBound.magnitude - upperBound.magnitude
+        : lowerBound.magnitude + upperBound.magnitude
+    } else {
+      delta = upperBound.magnitude - lowerBound.magnitude
+    }
+    if delta == Bound.Magnitude.max {
+      return Bound(truncatingIfNeeded: generator.next() as Bound.Magnitude)
+    }
+    delta += 1
+    let randomMagnitude = generator.next(upperBound: delta)
+    if sameSign {
+      return lowerBound + Bound(randomMagnitude)
+    } else {
+      return Bound.isSigned && randomMagnitude <= upperBound.magnitude
+        ? Bound(randomMagnitude)
+        : 0 - Bound(randomMagnitude - upperBound.magnitude)
+    }
+  }
+}
+
 extension ClosedRange {
   @_inlineable
   public func overlaps(_ other: ClosedRange<Bound>) -> Bool {

diff --git a/stdlib/public/core/Integers.swift.gyb b/stdlib/public/core/Integers.swift.gyb
@@ -2344,7 +2344,7 @@ ${assignmentOperatorComment(x.operator, False)}
   % end
 }
 
-% for Range in ['CountableRange', 'CountableClosedRange']:
+% for Range in ['Range', 'ClosedRange']:
 
 extension FixedWidthInteger
 where Self.Stride : SignedInteger,

diff --git a/stdlib/public/core/Random.swift b/stdlib/public/core/Random.swift
@@ -85,7 +85,7 @@ extension RandomNumberGenerator {
 /// Using the preferred way:
 ///
 ///     let random = UInt8.random(in: .min ... .max)
-///     let randomToTen = UInt32.random(in: 0 ... 128)
+///     let randomToTen = UInt32.random(in: 0 ..< 10)
 ///
 /// - Note: The default implementation of randomness is cryptographically secure.
 ///   It utilizes arc4random(3) on newer versions of macOS, iOS, etc. On older

diff --git a/stdlib/public/core/Range.swift b/stdlib/public/core/Range.swift
@@ -266,6 +266,56 @@ extension Range where Bound: Strideable, Bound.Stride : SignedInteger {
   }
 }
 
+extension Range
+where Bound : FixedWidthInteger,
+      Bound.Magnitude : UnsignedInteger {
+
+  /// Returns a random element from this collection.
+  ///
+  /// - Parameter generator: The random number generator to use when getting
+  ///   a random element.
+  /// - Returns: A random element from this collection.
+  ///
+  /// A good example of this is getting a random greeting from an array:
+  ///
+  ///     let greetings = ["hi", "hey", "hello", "hola"]
+  ///     let randomGreeting = greetings.random()
+  ///
+  /// If the collection is empty, the value of this function is `nil`.
+  ///
+  ///     let numbers = [10, 20, 30, 40, 50]
+  ///     if let randomNumber = numbers.random() {
+  ///         print(randomNumber)
+  ///     }
+  ///     // Could print "20", perhaps
+  @_inlineable
+  public func random(
+    using generator: RandomNumberGenerator = Random.default
+  ) -> Element? {
+    guard lowerBound != upperBound else {
+      return nil
+    }
+    let isLowerNegative = Bound.isSigned && lowerBound < 0
+    let sameSign = !Bound.isSigned || isLowerNegative == (upperBound < 0)
+    let delta: Bound.Magnitude
+    if isLowerNegative {
+      delta = sameSign
+        ? lowerBound.magnitude - upperBound.magnitude
+        : lowerBound.magnitude + upperBound.magnitude
+    } else {
+      delta = upperBound.magnitude - lowerBound.magnitude
+    }
+    let randomMagnitude = generator.next(upperBound: delta)
+    if sameSign {
+      return lowerBound + Bound(randomMagnitude)
+    } else {
+      return randomMagnitude < upperBound.magnitude
+        ? Bound(randomMagnitude)
+        : -1 - Bound(randomMagnitude - upperBound.magnitude)
+    }
+  }
+}
+
 extension Range: RangeExpression {
   @_inlineable // FIXME(sil-serialize-all)
   public func relative<C: Collection>(to collection: C) -> Range<Bound>