flatMap.gyb

% for Kind in Kinds:
%Minimal = 'Minimal' + Kind

${Test}.test("flatMap/${Kind}/Lazy") {
  for test in flatMapTests {
    let s = ${Minimal}<OpaqueValue<Int>>(
      elements: test.sequence.map(OpaqueValue.init))
    let closureLifetimeTracker = LifetimeTracked(0)
    var timesClosureWasCalled = 0

    var result = s.lazy.flatMap {
      (element: OpaqueValue<Int>) -> ${Minimal}<OpaqueValue<Int32>> in
      _blackHole(closureLifetimeTracker)
      timesClosureWasCalled += 1
      let elements = test.transform(element.value)
      return ${Minimal}<OpaqueValue<Int32>>(
        elements: elements.map { OpaqueValue($0) })
    }
    expectEqual(0, timesClosureWasCalled, "Unexpected eagerness")

%   if Kind == 'Sequence':
    let expected = test.expected.map(OpaqueValue.init)
    check${Kind}(expected, result,
      stackTrace: SourceLocStack().with(test.loc),
      resiliencyChecks: .none
    ) { $0.value == $1.value }
    expectEqual(
      test.sequence.count, timesClosureWasCalled,
      "iterating forward the result of the lazy flatMap() should call "
      + "the closure only once for element")
%   else:
    _ = Array(result)
    /*
    FIXME: this check is failing.
    This is a fundamental problem with lazy flatMap().
    <rdar://problem/21989896> Investigate other Collection schemes: indices
    are compositions of offsets

    expectEqual(
      test.sequence.count, timesClosureWasCalled,
      "iterating forward the result of the lazy flatMap() should call "
      + "the closure only once for element")
    */

    // FIXME: we are not calling check${Kind} because of the same issue again.
    // <rdar://problem/21989896>
    let expected = test.expected.map(OpaqueValue.init)
    expectEqualSequence(
      expected, result,
      stackTrace: SourceLocStack().with(test.loc)
    ) { $0.value == $1.value }
%   end

    % if Kind == 'Sequence':
    expectTrue(Array(s).isEmpty, "sequence should be consumed")
    expectEqual(
      test.sequence.count, timesClosureWasCalled,
      "iterating a lazy flatMap() should call the predicate"
      + "once per element")
    % end
  }

  for test in flatMapToOptionalTests {
    let s = ${Minimal}<OpaqueValue<Int>>(elements:
      test.sequence.map(OpaqueValue.init))
    let closureLifetimeTracker = LifetimeTracked(0)
    var timesClosureWasCalled = 0

    var result = s.lazy.flatMap {
      (element: OpaqueValue<Int>) -> OpaqueValue<Int32>? in
      _blackHole(closureLifetimeTracker)
      timesClosureWasCalled += 1
      return test.transform(element.value).map(OpaqueValue.init)
    }
    expectEqual(0, timesClosureWasCalled, "unexpected eagerness")

    let expected = test.expected.map(OpaqueValue.init)
    expectEqualSequence(
      expected, result,
      stackTrace: SourceLocStack().with(test.loc)
    ) { $0.value == $1.value }
    expectEqual(
      test.sequence.count, timesClosureWasCalled,
      "iterating lazy flatMap() should call closure once per element")
  }
}
% end