LanguageFeatures/Generic-functions-as-type-args/typedef3_A01_t05.dart

// Copyright (c) 2021, 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 Allow generic function types as type arguments and bounds
///
/// The language disallows generic function types as type arguments and bounds.
///
///  late List<T Function<T>(T)> idFunctions; // INVALID.
///  var callback = [foo<T>(T value) => value]; // Inferred as above, then invalid.
///  late S Function<S extends T Function<T>(T)>(S) f; // INVALID.
///
/// We remove that restriction, so a type argument and a bound can be a generic
/// function type.
///
/// This requires no new syntax, and in some cases only the removal of a single
/// check. There might be some platforms where the implementation currently
/// assumes that generic function types cannot occur as the value of type
/// variables (an proof-of-concept attempt hit an assert in the VM). Such
/// assumptions will need to be flushed out with tests and fixed.
///
/// Because we already infer List<T Function<T>(T)> in the code above, this
/// change will not affect type inference, it will just make the inferred type
/// not be an error afterwards.
///
/// We do not expect the removal of this restriction to affect the feasibility of
/// type inference. After all, it's already possible to have a generic function
/// type occurring covariantly in a type argument, like List<T Function<T>(T)
/// Function()>.
/// @description Checks that generic function can be a non-function typedef type
/// argument and bound: test extends clause in the typedef declaration
/// statically.
/// @Issue 45065
/// @author iarkh@unipro.ru


typedef exp1 = T Function<T>(T);
typedef exp2 = void Function<T>();
typedef exp3 = T Function<T>();
typedef exp4 = void Function<T>(T);

class C<T> {}

typedef C1<X extends exp3> = C<X>;

test1() {
  C1 c = C1<int>();
//       ^
// [analyzer] unspecified
// [cfe] unspecified

  C1 c1 = C1<exp1>();
//        ^
// [analyzer] unspecified
// [cfe] unspecified

  C1 c2 = C1<exp2>();
//        ^
// [analyzer] unspecified
// [cfe] unspecified

  C1 c3 = C1<exp3>();

  C1 c4 = C1<exp4>();
//        ^
// [analyzer] unspecified
// [cfe] unspecified
}

test2() {
  C1<int>();
//   ^
// [analyzer] unspecified
// [cfe] unspecified

  C1<exp1>();
//   ^
// [analyzer] unspecified
// [cfe] unspecified

  C1<exp2>();
//   ^
// [analyzer] unspecified
// [cfe] unspecified

  C1<exp3>();

  C1<exp4>();
//   ^
// [analyzer] unspecified
// [cfe] unspecified
}

main() {}