Conditionally conform EnumeratedSequence to Collections

stdlib/public/core/Algorithm.swift

@@ -74,91 +74,3 @@ public func max<T: Comparable>(_ x: T, _ y: T, _ z: T, _ rest: T...) -> T {
   }
   return maxValue
 }
-
-/// An enumeration of the elements of a sequence or collection.
-///
-/// `EnumeratedSequence` is a sequence of pairs (*n*, *x*), where *n*s are
-/// consecutive `Int` values starting at zero, and *x*s are the elements of a
-/// base sequence.
-///
-/// To create an instance of `EnumeratedSequence`, call `enumerated()` on a
-/// sequence or collection. The following example enumerates the elements of
-/// an array.
-///
-///     var s = ["foo", "bar"].enumerated()
-///     for (n, x) in s {
-///         print("\(n): \(x)")
-///     }
-///     // Prints "0: foo"
-///     // Prints "1: bar"
-@frozen
-public struct EnumeratedSequence<Base: Sequence> {
-  @usableFromInline
-  internal var _base: Base
-
-  /// Construct from a `Base` sequence.
-  @inlinable
-  internal init(_base: Base) {
-    self._base = _base
-  }
-}
-
-extension EnumeratedSequence: Sendable where Base: Sendable {}
-
-extension EnumeratedSequence {
-  /// The iterator for `EnumeratedSequence`.
-  ///
-  /// An instance of this iterator wraps a base iterator and yields
-  /// successive `Int` values, starting at zero, along with the elements of the
-  /// underlying base iterator. The following example enumerates the elements of
-  /// an array:
-  ///
-  ///     var iterator = ["foo", "bar"].enumerated().makeIterator()
-  ///     iterator.next() // (0, "foo")
-  ///     iterator.next() // (1, "bar")
-  ///     iterator.next() // nil
-  ///
-  /// To create an instance, call
-  /// `enumerated().makeIterator()` on a sequence or collection.
-  @frozen
-  public struct Iterator {
-    @usableFromInline
-    internal var _base: Base.Iterator
-    @usableFromInline
-    internal var _count: Int
-
-    /// Construct from a `Base` iterator.
-    @inlinable
-    internal init(_base: Base.Iterator) {
-      self._base = _base
-      self._count = 0
-    }
-  }
-}
-
-extension EnumeratedSequence.Iterator: Sendable where Base.Iterator: Sendable {}
-
-extension EnumeratedSequence.Iterator: IteratorProtocol, Sequence {
-  /// The type of element returned by `next()`.
-  public typealias Element = (offset: Int, element: Base.Element)
-
-  /// Advances to the next element and returns it, or `nil` if no next element
-  /// exists.
-  ///
-  /// Once `nil` has been returned, all subsequent calls return `nil`.
-  @inlinable
-  public mutating func next() -> Element? {
-    guard let b = _base.next() else { return nil }
-    let result = (offset: _count, element: b)
-    _count += 1 
-    return result
-  }
-}
-
-extension EnumeratedSequence: Sequence {
-  /// Returns an iterator over the elements of this sequence.
-  @inlinable
-  public __consuming func makeIterator() -> Iterator {
-    return Iterator(_base: _base.makeIterator())
-  }
-}