Implement 'Collection.count'

StandardLibrary/Sources/Core/Collection.hylo

@@ -28,6 +28,15 @@ public trait Collection {
 
 public extension Collection {
 
+  /// Returns the number of elements in `self`.
+  ///
+  /// - Complexity: O(n), where n is the number of elements in `self`.
+  public fun count() -> Int {
+    var r = 0
+    for let _ in self { &r += 1 }
+    return r
+  }
+
   /// Returns the result of applying `combine` on an accumulator, initialized with `initial_value`,
   /// and each element of `self`, in order.
   ///

Tests/LibraryTests/TestCases/CollectionTests.hylo

@@ -1,5 +1,23 @@
 //- compileAndRun expecting: .success
 
+conformance Int: Collection {
+
+  public typealias Element = Bool
+  public typealias Position = Int
+
+  public fun start_position() -> Int { 0 }
+  public fun end_position() -> Int { Int.bit_width() }
+  public fun position(after p: Int) -> Int { p + 1 }
+
+  public subscript(_ p: Int): Bool { (self & (1 << p)) != 0 }
+
+}
+
+fun test_count() {
+  let a = 0
+  precondition(a.count() == 64)
+}
+
 fun test_reduce() {
   var a = Array<Int>()
   &a.append(1)
@@ -31,6 +49,7 @@ fun test_all_satisfy() {
 }
 
 public fun main() {
+  test_count()
   test_reduce()
   test_contains_where()
   test_all_satisfy()