Paul Berry
2b8411f626
This language feature allows type promotion to apply to private final
fields, e.g.:
class C {
final int? _x;
C(this._x);
}
f(C c) {
if (c._x != null) {
print(c._x.abs()); // (1)
}
}
Previously the line marked (1) would have needed to be written
`print(c._x!.abs());`.
Note that to ensure soundness, there are certain restrictions:
- Public fields don't undergo promotion (because a public field might
be overridden by a class in some other library).
- Non-final fields don't undergo promotion (because a non-final field
might be modified as a side effect of code executed between the type
test and the field's usage).
- Fields that are forwarded to `noSuchMethod` in the same library
don't undergo promotion (because there's no guarantee that
`noSuchMethod` will return the same value on every invocation). For
example:
class C {
final int? _x;
C(this._x);
}
class D implements C {
@override
noSuchMethod(...) => ...;
}
f(C c) {
if (c._x != null) {
print(c._x.abs()); // ERROR: `c._x` might dispatch to
// `D.noSuchMethod`, in which case there's
// no guarantee that it will return a
// non-null value the second time it's
// invoked.
}
}
- If two classes define fields or getters of the same name, and
promotion is not permitted for one of them, then it isn't permitted
for the other. This is because there might be a class in some other
library that's a subclass of both classes, causing a reference to
one field or getter to dispatch to the other. For example:
class C {
final int? _x;
C(this._x);
}
class D {
int? get _x => ...;
}
f(C c) {
if (c._x != null) {
print(c._x.abs()); // ERROR: `c._x` might dispatch to `D._x`
// (e.g. because some library might declare
// `class E extends D implements C`), in
// which case there's no guarantee that it
// will return a non-null value the second
// time it's invoked.
}
}
Change-Id: Ib9183581aa0194377e38ab70d37c3e9f0bb57a75
Bug: https://github.com/dart-lang/language/issues/2020
Tested: TAP global presubmit
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/314600
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Nate Bosch <nbosch@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>
FE/analyzer shared code
This package contains logic that is shared between the front_end and analyzer packages. It is intended solely to facilitate development of the Dart SDK, and is not intended for use by end users. In particular, this package has no public API, so no guarantee is made of compatibility between one version of the package and the next.
End users should consider using the analyzer package to analyze Dart source code.