Denis Zharkov
406e31f54a
Mostly this commit is about skipping wildcards that are redundant in some sense.
The motivation is that they looks `long` in Java code.
There are basically two important parts: return types and value parameters.
1. For return types default behaviour is skipping all declaration-site wildcards.
The intuition behind this rule is simple: return types are basically used in subtype position
(as an argument for another call), and here everything works well in case of 'out'-variance.
For example we have 'Out<Out<T>>>' as subtype both for 'Out<Out<T>>>' and 'Out<? extends Out<? extends T>>>',
so values of such type is more flexible in contrast to `Out<? extends Out<? extends T>>>` that could be used only
for the second case.
But we have choosen to treat `in`-variance in a different way: argument itself
should be rendered without wildcard while nested arguments are rendered by the rules
described further (see second part).
For example: 'In<Out<OpenClass>>' will have generic signature 'In<Out<? extends OpenClass>>'.
If we omit all wildcards here, then value of type 'In<Out<OpenClass>>'
will be impossible to use as argument for function expecting 'In<? super Out<? extends Derived>>'
where Derived <: OpenClass (you can check it manually :]).
And this exception should not be very inconvinient because in-variance is rather rare.
2. For value parameters we decided to skip wildcards if it doesn't make obtained signature weaker
in a sense of set of acceptable arguments.
More precisely:
a. We write wildcard for 'Out<T>' iff T ``can have subtypes ignoring nullability''
b. We write wildcard for 'In<T>' iff T is not equal to it's class upper bound (ignoring nullability again)
Definition of ``can have subtypes ignoring nullability'' is straightforward and you can see it in commit.
#KT-9801 Fixed
#KT-9890 Fixed
26 lines
1.0 KiB
Kotlin
Vendored
26 lines
1.0 KiB
Kotlin
Vendored
class Out<out T>
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class OutPair<out X, out Y>
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class In<in Z>
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class Final
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open class Open
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// For value parameters we decided to skip wildcards if it doesn't make obtained signature weaker
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// in a sense of set of acceptable arguments.
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// More precisely:
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// a. We write wildcard for 'Out<T>' iff T ``can have subtypes ignoring nullability''
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// b. We write wildcard for 'In<T>' iff T is not equal to it's class upper bound (ignoring nullability again)
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// Definition of ``can have subtypes ignoring nullability'' is straightforward and you can see it in commit.
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fun openClassArgument(x: Out<Open>, y: In<Open>) {}
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// method: ArgumentOverridabilityKt::openClassArgument
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// generic signature: (LOut<+LOpen;>;LIn<-LOpen;>;)V
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fun finalClassArgument(x: Out<Final>, y: In<Final>) {}
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// method: ArgumentOverridabilityKt::finalClassArgument
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// generic signature: (LOut<LFinal;>;LIn<-LFinal;>;)V
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fun oneArgumentFinal(x: OutPair<Final, Open>) {}
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// method: ArgumentOverridabilityKt::oneArgumentFinal
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// generic signature: (LOutPair<LFinal;+LOpen;>;)V
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