Add conditional lazy conformances

Author: natecook1000

Sources/Algorithms/AdjacentPairs.swift

@@ -69,6 +69,7 @@ public struct AdjacentPairsSequence<Base: Sequence> {
 }
 
 extension AdjacentPairsSequence {
+  /// The iterator for an `AdjacentPairsSequence` or `AdjacentPairsCollection`.
   public struct Iterator {
     @usableFromInline
     internal var base: Base.Iterator
@@ -113,6 +114,9 @@ extension AdjacentPairsSequence: Sequence {
   }
 }
 
+extension AdjacentPairsSequence: LazySequenceProtocol
+  where Base: LazySequenceProtocol {}
+
 /// A collection of adjacent pairs of elements built from an underlying
 /// collection.
 ///
@@ -159,6 +163,7 @@ extension AdjacentPairsCollection {
 }
 
 extension AdjacentPairsCollection {
+  /// A position in an `AdjacentPairsCollection`.
   public struct Index: Comparable {
     @usableFromInline
     internal var first: Base.Index
@@ -299,6 +304,9 @@ extension AdjacentPairsCollection: BidirectionalCollection
 extension AdjacentPairsCollection: RandomAccessCollection
   where Base: RandomAccessCollection {}
 
+extension AdjacentPairsCollection: LazySequenceProtocol, LazyCollectionProtocol
+  where Base: LazyCollectionProtocol {}
+
 extension AdjacentPairsCollection.Index: Hashable where Base.Index: Hashable {
   @inlinable
   public func hash(into hasher: inout Hasher) {

Tests/SwiftAlgorithmsTests/AdjacentPairsTests.swift

@@ -72,4 +72,9 @@ final class AdjacentPairsTests: XCTestCase {
   func testIndexTraversals() {
     validateIndexTraversals((1...5).adjacentPairs())
   }
+  
+  func testLaziness() {
+    XCTAssertLazySequence((0...).lazy.adjacentPairs())
+    XCTAssertLazyCollection((0..<100).lazy.adjacentPairs())
+  }
 }