Revert Optional<T extends Object> to Optional<T> #667
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Optional is intended as a substitute for non-nullable values. Ideally, it should have a generic type of `T extends Object` in order to prevent non-sensical declarations like `Optional<Foo?>`. Such declarations are unlikely to happen intentionally, but one could imagine the case of an Optional<T> used in another generic class, where T is a nullable type. In google#652, we prevented such uses by declaring Optional as Optional<T extends Object>. This turns out to be a significant breaking change, since previously, T implicitly extended `dynamic` and therefore checks like the following didn't produce any analysis errors: if (obj is Optional) { return obj.value.someMethod(); } where `someMethod` is a method defined on `T`. A survey of the Google codebase suggests this would be a fairly extensive breaking change. Given that Optional makes little sense once null-safety is enabled in the language by default, the simpler change may simply be to leave as-is and deprecate the class once null-safety lands in the language. It appears that there are no checks on the return type of `transform`, and this seems significantly unlikely, therefore we leave that change in place. This partially reverts 28301f9. Related: google#666
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Optional is intended as a substitute for non-nullable values. Ideally, it should have a generic type of `T extends Object` in order to prevent non-sensical declarations like `Optional<Foo?>`. Such declarations are unlikely to happen intentionally, but one could imagine the case of an Optional<T> used in another generic class, where T is a nullable type. In #652, we prevented such uses by declaring Optional as Optional<T extends Object>. This turns out to be a significant breaking change, since previously, T implicitly extended `dynamic` and therefore checks like the following didn't produce any analysis errors: if (obj is Optional) { return obj.value.someMethod(); } where `someMethod` is a method defined on `T`. A survey of the Google codebase suggests this would be a fairly extensive breaking change. Given that Optional makes little sense once null-safety is enabled in the language by default, the simpler change may simply be to leave as-is and deprecate the class once null-safety lands in the language. It appears that there are no checks on the return type of `transform`, and this seems significantly unlikely, therefore we leave that change in place. This partially reverts 28301f9. Related: #666
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Optional is intended as a substitute for non-nullable values. Ideally,
it should have a generic type of
T extends Objectin order to preventnon-sensical declarations like
Optional<Foo?>. Such declarations areunlikely to happen intentionally, but one could imagine the case of an
Optional used in another generic class, where T is a nullable type.
In #652, we prevented such uses by declaring Optional as
Optional.
This turns out to be a significant breaking change, since previously, T
implicitly extended
dynamicand therefore checks like the followingdidn't produce any analysis errors:
where
someMethodis a method defined onT.A survey of the Google codebase suggests this would be a fairly
extensive breaking change. Given that Optional makes little sense once
null-safety is enabled in the language by default, the simpler change
may simply be to leave as-is and deprecate the class once null-safety
lands in the language.
It appears that there are no checks on the return type of
transform,and this seems significantly unlikely, therefore we leave that change in
place.
This partially reverts 28301f9.
Related: #666
Related: #606