Pavel V. Talanov
67 lines
2.3 KiB
Markdown
67 lines
2.3 KiB
Markdown
# Support for JVM's ACC_NATIVE flag
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Goal: enable JNI interop for Kotlin, so that anything that works through JNI in Java could be reproduced 1-to-1 in Kotlin
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## Syntax
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The following definition is present in the library:
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``` kotlin
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package kotlin.jvm
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Retention(RetentionPolicy.SOURCE)
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public annotation class native
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```
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This annotation is applicable to
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- functions
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- property accessors
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A declaration marked with this annotation is referred to as a *native declaration*.
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Checks to perform:
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- a native declaration can not be abstract
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- a native declaration can not have a body
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- a native declaration can not be marked `inline`
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- a native declaration can not have `reified` type parameters
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NOTE: this is achieved through prohibiting `inline`, as `reified` is only allowed on inline-functions now
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- members of traits can not be native
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NOTE: native members can override open (or abstract) members of supertypes
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## Semantics on the JVM
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Intuition: a JVM method whose source declaration is native is marked with the `ACC_NATIVE` flag, and has no `CODE` attribute.
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### Interaction with \[platformStatic\]
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A native member of an object marked `native` and `platformStatic` is translated in a straightforward way:
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there is only one JVM method corresponding to it, and it is marked as `ACC_NATIVE`.
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A member of a companion object of class `C` marked `native` and `platformStatic` yields two JVM methods:
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- static member of `C` that is marked `ACC_NATIVE`;
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- instance member of `C$object` that is not marked `ACC_NATIVE` and its body delegates to the native static method.
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### Top-level declarations
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A native member of package `p` yields one JVM method:
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- member of a package-facade class `PPackage` which is marked with `ACC_NATIVE` flag.
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### Native Property Accessors
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A property can not be marked `native`.
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A *property accessor* can be marked `native` if it has no body (i.e. it is a *default accessor*).
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In this case the generated code is the same as for a native function defined in the same context as the property.
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Example:
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``` kotlin
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val foo: Int
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[native] get
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```
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## Not implemented (yet)
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- native property accessors
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- frontend: when accessors are default and native, don't require an initializer, don't allow a backing field
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- backend: when accessors are default and native, don't generate a backing field
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- applicability checks: only functions and property accessors |