Paul Berry
c4de71ede2
Original description: Change front_end handling of callable classes. This CL is the first in a series of CLs to change the handling of callable classes in Dart 2.0. For purposes of this description, a "callable class" is a class whose interface contains a `.call` method. In Dart 1.0, a callable class was considered to be a subtype of the `.call` method's function type. This allowed the user to create custom objects with similar behavior to closures, but with additional fields and methods. In Dart 2.0, a callable class is just an ordinary class, with no subtype relation to any particular function type. (Note however that it is still permissible for a class to declare that it "implements Function"). To reduce the amount of code broken by this change, a piece of syntactic sugar is being added: if an expression whose static type is a callable class appears where a function type is expected, an implicit tear-off of the `.call` method is inserted. Note that it is still possible at compile time to invoke an expression whose static type is a callable class, and it is still possible at runtime to invoke an expression whose runtime type is a callable class; in both cases, this is considered an implicit invocation of the class's `.call` method. This is unchanged from Dart 1.0 behavior. This CL introduces test cases for the new behavior, and implements the implicit tear-off of `.call` in the front end. Still to be implemented in future CLs: - Spec text needs to be written. - DDC/analyzer code needs to be written to perform implicit tear-offs of `.call`. - The subtyping algorithm in DDC, analyzer, VM, and dart2js needs to be changed so that callable classes are no longer considered subtypes of any particular function type. - A small corner case involving type parameters still needs to be addressed (see TODO in pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart). Fixes #32064. Change-Id: I0d397c608321e25ba42cc02aa8a516aa77aa7c9d Reviewed-on: https://dart-review.googlesource.com/41280 Reviewed-by: Vyacheslav Egorov <vegorov@google.com> Commit-Queue: Paul Berry <paulberry@google.com>
30 lines
657 B
Dart
30 lines
657 B
Dart
// Copyright (c) 2018, 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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// Dart test program to test arithmetic operations.
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class B {}
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class C {
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B call(B b) => b;
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}
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typedef B BToB(B x);
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class D {
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BToB f() => null;
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void g(C x) {}
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}
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class E extends D {
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// This override is illegal because C is not a subtype of BToB.
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C f() => null; //# 01: compile-time error
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// This override is illegal because BToB is not a supertype of C.
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void g(BToB x) {} //# 02: compile-time error
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}
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main() {
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new E();
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}
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