Add KEEP for sealed inline classes #312
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proposals/sealed-inline-classes.md
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| ## Motivation / use cases | ||
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| The main use-case for sealed inline classes is `Result`. Currently it is decraled as inline class with underlying type `Any?` |
proposals/sealed-inline-classes.md
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| This is the reason for the following restrictions. | ||
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| - Noinline children (classes and objects) should have `value` modifier, as shown in the examples. Since the noinline children can be boxed, they cannot have stable identity. In other words, they are identitiless, and we use `value` modifier to mark them. |
proposals/sealed-inline-classes.md
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| `<hash>` is computed using usual [inline classes mangling rules](https://github.com/Kotlin/KEEP/blob/master/proposals/inline-classes.md#mangling-rules). | ||
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| - When we pass nullable sealed inline class, it is mapped to boxed selaed inline class: |
proposals/sealed-inline-classes.md
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| the compiler generates the following code | ||
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| ```kotlin | ||
| val ic = Integet.valueOf(1) |
proposals/sealed-inline-classes.md
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| val ic = Integet.valueOf(1) | ||
| ``` | ||
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| The following rulues for passing to function and returning from the function apply: |
proposals/sealed-inline-classes.md
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| fun `toString-impl`(value: Any?): String = "I3${`$value`}" | ||
| ``` | ||
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| The logic for `toString` applies for all methods, decrared in interfaces: if the method is not overridden in inline child, we do not generate redirect. |
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| ```kotlin | ||
| // In I1 | ||
| synthetic fun `str-impl`(value: Any?): String = I2.`str-impl`(value) |
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synthetic has been used inconsistently in the examples.
See the following lines or the definition of the $value property.
proposals/sealed-inline-classes.md
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| ```kotlin | ||
| class IC { | ||
| val $value: Any? |
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Is this a Kotlin property?
We should expect on JVM?
private Object $value
public Object get$value()
| * **Status**: Experimental | ||
| * **Prototype**: TODO | ||
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| Discussion of this proposal is held in [this issue](TODO). |
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Please, create an issue for discussion.
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| The changes also rely on [inline classes with generic underlying value](https://youtrack.jetbrains.com/issue/KT-32162/Allow-generics-for-inline-classes). | ||
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| So, to create the `Result` value one will use constructors instead of factory functions. In other words, instead of |
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We should have a separate design discussion on whether we shall deprecate Result.success and Result.failure in favor or Result.Success and Result.Failure constructors. Please, add it to open issues.
| } | ||
| ``` | ||
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| here, we can use `Number` as the underlying type. However, adding non-`Number` child will change the underlying type, |
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It is better to replace "we can use Number" with "we could have used Number" to let a reader understand what's the actual design we are going with and what is just a digression on other potential alternatives we have considered in the design.
| ``` | ||
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| ## Is checks | ||
| Consider the following example |
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This example does not compile because sealed inline class child cannot be distinguished from another one
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| - If sealed inline class is a child of another sealed inline class, there can be no other inline children, including other sealed inline class, since sealed inline classes are mapped to `Any?`, which is open class, which other classes override and there is no way to distinguish `Any?` from other type. | ||
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| - Value objects must be a child of sealed inline class. |
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The proposal doesn't explain what a "value object" is and when it's allowed
| ``` | ||
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| Note, that `O2` does not override `toString`, so we should call `Any.toString()` | ||
| is case of `O2`, since `I2` does not override `toString` as well. |
| @JvmInline | ||
| sealed value class I2 : I1() | ||
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| sealed object O1: I1() { |
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Shouldn't be value object instead of sealed object here?
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