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ltOgt/maybeFuture.dart

Last active August 2, 2023 15:50
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check if future
Raw
maybeFuture.dart
import 'dart:async';
typedef _Future = Future Function();
typedef _Void = void Function();
typedef _FutureOrVoid = FutureOr<void> Function();
main () {
_FutureOrVoid f;
f = () async {};
print(f is _Future); // true
print(f is _Void); // TRUE
print(f is _FutureOrVoid); // TRUE
f = () {};
print(f is _Future); // false
print(f is _Void); // TRUE
print(f is _FutureOrVoid); // TRUE
}
// ===============
import 'dart:async';
typedef FutureInt = Future<int> Function();
typedef Int = int Function();
typedef FutureOrInt = FutureOr<int> Function();
main () {
Base either;
either = InstanceFuture();
print(either.isFuture); // true
print(either.f is FutureInt); // true
print(resolveOpaqueFutureInt() is FutureInt); // true
either = InstanceInt();
print(either.isFuture); // false
print(either.f is FutureInt); // false
print(resolveOpaqueInt() is FutureInt); // false
}
// always chooses first but is opaque
FutureOrInt resolveOpaqueFutureInt() => DateTime.now().isAfter(DateTime.fromMicrosecondsSinceEpoch(0))
? (InstanceFuture() as Base).f
: (InstanceInt() as Base).f;
// always chooses second but is opaque
FutureOrInt resolveOpaqueInt() => DateTime.now().isBefore(DateTime.fromMicrosecondsSinceEpoch(0))
? (InstanceFuture() as Base).f
: (InstanceInt() as Base).f;
abstract class Base {
FutureOrInt get f;
bool get isFuture => f is FutureInt;
}
class InstanceFuture extends Base {
@override
FutureInt get f => () async => 1;
}
class InstanceInt extends Base {
@override
Int get f => () => 1;
}
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