Use forEach() and fix tests

Author: Russ Bishop

stdlib/private/StdlibCollectionUnittest/CheckSequenceType.swift

@@ -127,7 +127,7 @@ public struct FindTest {
   ) {
     self.expected = expected
     self.element = MinimalEquatableValue(element)
-    self.sequence = sequence.enumerate().map {
+    self.sequence = sequence.enumerated().map {
       return MinimalEquatableValue($1, identity: $0) 
     }
     self.expectedLeftoverSequence = expectedLeftoverSequence.map(
@@ -1777,21 +1777,21 @@ self.test("\(testNamePrefix).forEach/semantics") {
 // first()
 //===----------------------------------------------------------------------===//
 
-SequenceTypeTests.test("\(testNamePrefix).first/semantics") {
+self.test("\(testNamePrefix).first/semantics") {
   for test in findTests {
-    let s = MinimalSequence<MinimalEquatableValue>(elements: test.sequence)
+    let s = makeWrappedSequenceWithEquatableElement(test.sequence)
     let closureLifetimeTracker = LifetimeTracked(0)
     let found = s.first {
       _blackHole(closureLifetimeTracker)
-      return $0 == test.element
+      return $0 == wrapValueIntoEquatable(test.element)
     }
     expectEqual(
-      test.expected == nil ? nil : test.element,
+      test.expected == nil ? nil : wrapValueIntoEquatable(test.element),
       found,
       stackTrace: SourceLocStack().with(test.loc))
-    if let found = found {
+    if test.expected != nil {
       expectEqual(
-        test.expected, found.identity,
+        test.expected, (found as? MinimalEquatableValue)?.identity,
         "find() should find only the first element matching its predicate")
     }
   }

stdlib/private/StdlibCollectionUnittest/LoggingWrappers.swift.gyb

@@ -249,7 +249,7 @@ public struct ${Self}<
     where predicate: @noescape (Base.Iterator.Element) throws -> Void
   ) rethrows -> Base.Iterator.Element? {
     Log.find[selfType] += 1
-    return base.find(where: predicate)
+    return try base.find(where: predicate)
   }
 
   public typealias SubSequence = Base.SubSequence

stdlib/public/core/Sequence.swift

@@ -968,7 +968,13 @@ extension Sequence {
       try body(element)
     }
   }
-  
+}
+
+private enum _StopIteration: ErrorProtocol {
+    case stop
+}
+
+extension Sequence {
   /// Returns the first element of the sequence that satisfies the given
   /// predicate or nil if no such element is found.
   ///
@@ -979,12 +985,16 @@ extension Sequence {
   public func first(
     where predicate: @noescape (Iterator.Element) throws -> Bool
   ) rethrows -> Iterator.Element? {
-    for element in self {
-      if try predicate(element) {
-        return element
+    var foundElement: Iterator.Element? = nil
+    do {
+      try self.forEach {
+        if try predicate($0) {
+          foundElement = $0
+          throw _StopIteration.stop
+        }
       }
-    }
-    return nil
+    } catch is _StopIteration { }
+    return foundElement
   }
 }
 

validation-test/stdlib/SequenceType.swift.gyb

@@ -950,7 +950,7 @@ SequenceTypeTests.test("forEach/dispatch") {
 
 SequenceTypeTests.test("first/dispatch") {
   let tester = SequenceLog.dispatchTester([OpaqueValue(1)])
-  tester.first { return $0.value == 1 }
+  tester.first { $0.value == 1 }
   expectCustomizable(tester, tester.log.first)
 }