LanguageFeatures/Records/type_inference_A01_t05.dart

// Copyright (c) 2022, 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 Given a type schema K and a record expression E of the general
/// form (e1, ..., en, d1 : e{n+1}, ..., dm : e{n+m}) inference proceeds as
/// follows.
///
/// If K is a record type schema of the form
/// (K1, ..., Kn, {d1 : K{n+1}, ...., dm : K{n+m}}) then:
///
/// - Each ei is inferred with context type schema Ki to have type Si
///   - Let Ri be the greatest closure of Ki
///   - If Si is a subtype of Ri then let Ti be Si
///   - Otherwise, if Si is dynamic, then we insert an implicit cast on ei to
///     Ri, and let Ti be Ri
///   - Otherwise, if Si is coercible to Ri (via some sequence of call method
///     tearoff or implicit generic instantiation coercions), then we insert the
///     appropriate implicit coercion(s) on ei. Let Ti be the type of the
///     resulting coerced value (which must be a subtype of Ri, possibly proper).
///   - Otherwise, it is a static error.
///  - The type of E is (T1, ..., Tn, {d1 : T{n+1}, ...., dm : T{n+m}})
/// If K is any other type schema:
///
/// - Each ei is inferred with context type schema _ to have type Ti
/// - The type of E is (T1, ..., Tn, {d1 : T{n+1}, ...., dm : T{n+m}})
///
/// @description Checks type inference for records.
/// @author sgrekhov22@gmail.com

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

class C<X> {
  Type get typeArgument => X;
}

class D<X extends Y, Y> extends C<Y> {}

main() {
  (C<int>, {C<double> x}) r = (D(), x: D());
  Expect.equals(int, r.$1.typeArgument);
  Expect.equals(double, r.x.typeArgument);
}