Robert Nystrom
d5bbfcd874
These changes look substantive to me, which isn't expected. Change-Id: Ie4e4fd9d702923b3c3c2fdd56160a523801a6c9f Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/162944 Commit-Queue: Erik Ernst <eernst@google.com> Reviewed-by: Erik Ernst <eernst@google.com>
92 lines
3.4 KiB
Dart
92 lines
3.4 KiB
Dart
// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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// Tests local inference errors for the `in` variance modifier.
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// SharedOptions=--enable-experiment=variance
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class Covariant<out T> {}
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class Contravariant<in T> {}
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class Exactly<inout T> {}
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class Upper {}
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class Middle extends Upper {}
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class Lower extends Middle {}
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class ContraBound<in T> {
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ContraBound(T x, void Function(T) y) {}
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}
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Exactly<T> inferCovContra<T>(Covariant<T> x, Contravariant<T> y) => new Exactly<T>();
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Exactly<T> inferContraContra<T>(Contravariant<T> x, Contravariant<T> y) => new Exactly<T>();
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Exactly<T> inferContraBound<T>(ContraBound<T> x) => new Exactly<T>();
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main() {
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Exactly<Upper> upper;
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Exactly<Lower> lower;
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// T <: Upper and T <: Middle.
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// We choose Middle.
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var inferredMiddle = inferContraContra(Contravariant<Upper>(), Contravariant<Middle>());
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upper = inferredMiddle;
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// ^^^^^^^^^^^^^^
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// [analyzer] COMPILE_TIME_ERROR.INVALID_ASSIGNMENT
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// [cfe] A value of type 'Exactly<Middle>' can't be assigned to a variable of type 'Exactly<Upper>'.
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// T <: Upper and T <: Lower.
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// We choose Lower.
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var inferredLower = inferContraContra(Contravariant<Upper>(), Contravariant<Lower>());
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upper = inferredLower;
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// ^^^^^^^^^^^^^
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// [analyzer] COMPILE_TIME_ERROR.INVALID_ASSIGNMENT
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// [cfe] A value of type 'Exactly<Lower>' can't be assigned to a variable of type 'Exactly<Upper>'.
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// int <: T <: String is not a valid constraint.
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inferCovContra(Covariant<int>(), Contravariant<String>());
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//^^^^^^^^^^^^^^
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// [analyzer] COMPILE_TIME_ERROR.COULD_NOT_INFER
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// [cfe] unspecified
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// String <: T <: int is not a valid constraint.
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inferCovContra(Covariant<String>(), Contravariant<int>());
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//^^^^^^^^^^^^^^
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// [analyzer] COMPILE_TIME_ERROR.COULD_NOT_INFER
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// [cfe] unspecified
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// Middle <: T <: Lower is not a valid constraint
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inferCovContra(Covariant<Middle>(), Contravariant<Lower>());
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//^^^^^^^^^^^^^^
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// [analyzer] COMPILE_TIME_ERROR.COULD_NOT_INFER
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// [cfe] unspecified
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// Upper <: T <: Lower is not a valid constraint
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inferCovContra(Covariant<Upper>(), Contravariant<Lower>());
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//^^^^^^^^^^^^^^
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// [analyzer] COMPILE_TIME_ERROR.COULD_NOT_INFER
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// [cfe] unspecified
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// Upper <: T <: Middle is not a valid constraint
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inferCovContra(Covariant<Upper>(), Contravariant<Middle>());
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//^^^^^^^^^^^^^^
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// [analyzer] COMPILE_TIME_ERROR.COULD_NOT_INFER
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// [cfe] unspecified
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// Inference for Contrabound(...) produces Lower <: T <: Upper.
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// Since T is contravariant, we choose Upper as the solution.
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var inferredContraUpper = inferContraBound(ContraBound(Lower(), (Upper x) {}));
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lower = inferredContraUpper;
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// ^^^^^^^^^^^^^^^^^^^
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// [analyzer] COMPILE_TIME_ERROR.INVALID_ASSIGNMENT
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// [cfe] A value of type 'Exactly<Upper>' can't be assigned to a variable of type 'Exactly<Lower>'.
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// Inference for Contrabound(...) produces Lower <: T <: Middle.
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// Since T is contravariant, we choose Middle as the solution.
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var inferredContraMiddle = inferContraBound(ContraBound(Lower(), (Middle x) {}));
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lower = inferredContraMiddle;
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// ^^^^^^^^^^^^^^^^^^^^
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// [analyzer] COMPILE_TIME_ERROR.INVALID_ASSIGNMENT
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// [cfe] A value of type 'Exactly<Middle>' can't be assigned to a variable of type 'Exactly<Lower>'.
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}
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