dart / co19 / refs/heads/master / . / LanguageFeatures / nnbd / weak / future_flattening_A01_t68.dart

// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file | |

// for details. All rights reserved. Use of this source code is governed by a | |

// BSD-style license that can be found in the LICENSE file. | |

/// @assertion The flatten function is modified as follows: | |

/// | |

/// [flatten(T)] is defined by cases on [T]: | |

/// | |

/// if [T] is [S?] then [flatten(T) = flatten(S)?] | |

/// otherwise if [T] is [S*] then [flatten(T) = flatten(S)*] | |

/// otherwise if [T] is [FutureOr<S>] then [flatten(T) = S] | |

/// otherwise [if T <: Future] then let [S] be a type such that [T <: | |

/// Future<S>] and for all [R], if [T <: Future<R>] then [S <: R]; then | |

/// [flatten(T) = S] | |

/// otherwise [flatten(T) = T] | |

/// | |

/// @description Check that future flattening works correctly for nullable | |

/// legacy [Future<A?>] type and the expression can be null. | |

/// | |

/// @author iarkh@unipro.ru | |

// Requirements=nnbd-weak | |

import "dart:async"; | |

import "../../../Utils/expect.dart"; | |

import "future_flattening_legacy_lib.dart"; | |

main() { | |

asyncStart(); | |

Future<A?>(() => null).then((value) => asyncEnd()); | |

asyncStart(); | |

Future<Future<A?>>(() => Future<A?>(() => null)).then((value) { | |

value.then((value1) => asyncEnd()); | |

}); | |

} |