| // Copyright (c) 2019, 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 Instantiate to bound then computes an actual type argument list |
| /// for [G] as follows: |
| /// |
| /// Let [Ui],[1] be [Si], for all [i] in [1 .. k]. (This is the "current value" |
| /// of the bound for type variable [i], at step [1]; in general we will |
| /// consider the current step, [m], and use data for that step, e.g., the bound |
| /// [Ui],[m], to compute the data for step [m + 1]). |
| /// |
| /// Let [-->m] be a relation among the type variables [X1 .. Xk] such that |
| /// [Xp -->m Xq] iff [Xq] occurs in [Up],[m] (so each type variable is related |
| /// to, that is, depends on, every type variable in its bound, possibly |
| /// including itself). Let [==>m] be the transitive closure of [-->m]. For each |
| /// [m], let [Ui],[m+1], for [i] in [1 .. k], be determined by the following |
| /// iterative process: |
| /// |
| /// 1. If there exists a [j] in [1 .. k] such that [Xj ==>m X0j] (that is, if |
| /// the dependency graph has a cycle) let [M1 .. Mp] be the strongly connected |
| /// components (SCCs) with respect to [-->m] (that is, the maximal subsets of |
| /// [X1 .. Xk] where every pair of variables in each subset are related in both |
| /// directions by [==>m]; note that the SCCs are pairwise disjoint; also, they |
| /// are uniquely defined up to reordering, and the order does not matter). Let |
| /// [M] be the union of [M1 .. Mp] (that is, all variables that participate in |
| /// a dependency cycle). Let [i] be in [1 .. k]. If [Xi] does not belong to [M] |
| /// then [Ui,m+1 = Ui,m]. Otherwise there exists a [q] such that [Xi] belongs |
| /// to [Mq]; [Ui,m+1] is then obtained from [Ui,m] by replacing every covariant |
| /// occurrence of a variable in [Mq] by [dynamic], and replacing every |
| /// contravariant occurrence of a variable in [Mq] by [Null]. |
| /// |
| /// 2. Otherwise, (if no dependency cycle exists) let [j] be the lowest number |
| /// such that [Xj] occurs in [Up,m] for some [p] and [Xj -/->m Xq] for all [q] |
| /// in [1..k] (that is, [Uj,m] is closed, that is, the current bound of [Xj] |
| /// does not contain any type variables; but [Xj] is being depended on by the |
| /// bound of some other type variable). Then, for all [i] in [1 .. k], [Ui,m+1] |
| /// is obtained from [Ui,m] by replacing every covariant occurrence of [Xj] by |
| /// [Uj,m], and replacing every contravariant occurrence of [Xj] by [Null]. |
| /// |
| /// 3. Otherwise, (when no dependencies exist) terminate with the result |
| /// [<U1,m ..., Uk,m>]. |
| /// @description Checks instantiation to bounds for [typedef A<X extends |
| /// FutureOr<C<X>?> = C<X>] |
| /// @author iarkh@unipro.ru |
| |
| import "dart:async"; |
| import "../../../../Utils/expect.dart"; |
| |
| class C<X> {} |
| typedef A<X extends FutureOr<C<X>?>> = C<X>; |
| |
| main() { |
| Expect.equals( |
| typeOf<C<FutureOr<C<dynamic>?>>>(), |
| typeOf<A>() |
| ); |
| } |