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Annotation Declaration
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annotation class Fancy
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annotation class Fancy
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@Target(AnnotationTarget.CLASS, AnnotationTarget.FUNCTION,
AnnotationTarget.VALUE_PARAMETER, AnnotationTarget.EXPRESSION)
@Retention(AnnotationRetention.SOURCE)
@MustBeDocumented
annotation class Fancy
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@Target(AnnotationTarget.CLASS, AnnotationTarget.FUNCTION,
AnnotationTarget.VALUE_PARAMETER, AnnotationTarget.EXPRESSION)
@Retention(AnnotationRetention.SOURCE)
@MustBeDocumented
annotation class Fancy
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Usage
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@Fancy class Foo {
@Fancy fun baz(@Fancy foo: Int): Int {
return (@Fancy 1)
}
}
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@Fancy class Foo {
@Fancy func baz(@Fancy foo: Int) -> Int {
return (@Fancy 1)
}
}
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class Foo @Inject constructor(dependency: MyDependency) { ... }
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class Foo @Inject constructor(dependency: MyDependency) { ... }
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class Foo {
var x: MyDependency? = null
@Inject set
}
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class Foo {
var x: MyDependency? = null
@Inject set
}
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Constructors
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annotation class Special(val why: String)
@Special("example") class Foo {}
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annotation class Special(let why: String)
@Special("example") class Foo {}
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annotation class ReplaceWith(val expression: String)
annotation class Deprecated(
val message: String,
val replaceWith: ReplaceWith = ReplaceWith(""))
@Deprecated("This function is deprecated, use === instead", ReplaceWith("this === other"))
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annotation class ReplaceWith(let expression: String)
annotation class Deprecated(
let message: String,
let replaceWith: ReplaceWith = ReplaceWith(""))
@Deprecated("This function is deprecated, use === instead", ReplaceWith("this === other"))
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import kotlin.reflect.KClass
annotation class Ann(val arg1: KClass<*>, val arg2: KClass<out Any>)
@Ann(String::class, Int::class) class MyClass
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import kotlin.reflect.KClass
annotation class Ann(let arg1: KClass<*>, let arg2: KClass<out Any>)
@Ann(String::class, Int::class) class MyClass
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Lambdas
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annotation class Suspendable
val f = @Suspendable { Fiber.sleep(10) }
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annotation class Suspendable
let f = @Suspendable { Fiber.sleep(10) }
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Annotation Use-site Targets
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class Example(@field:Ann val foo, // annotate Java field
@get:Ann val bar, // annotate Java getter
@param:Ann val quux) // annotate Java constructor parameter
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class Example(@field:Ann let foo, // annotate Java field
@get:Ann let bar, // annotate Java getter
@param:Ann let quux) // annotate Java constructor parameter
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@file:JvmName("Foo")
package org.jetbrains.demo
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@file:JvmName("Foo")
package org.jetbrains.demo
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class Example {
@set:[Inject VisibleForTesting]
var collaborator: Collaborator
}
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class Example {
@set:[Inject VisibleForTesting]
var collaborator: Collaborator
}
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fun @receiver:Fancy String.myExtension() { ... }
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func @receiver:Fancy String.myExtension() { ... }
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Java Annotations
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import org.junit.Test
import org.junit.Assert.*
import org.junit.Rule
import org.junit.rules.*
class Tests {
// apply @Rule annotation to property getter
@get:Rule val tempFolder = TemporaryFolder()
@Test fun simple() {
val f = tempFolder.newFile()
assertEquals(42, getTheAnswer())
}
}
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import org.junit.Test
import org.junit.Assert.*
import org.junit.Rule
import org.junit.rules.*
class Tests {
// apply @Rule annotation to property getter
@get:Rule let tempFolder = TemporaryFolder()
@Test func simple() {
let f = tempFolder.newFile()
assertEquals(42, getTheAnswer())
}
}
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// Java
public @interface Ann {
int intValue();
String stringValue();
}
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// Java
public @interface Ann {
int intValue();
String stringValue();
}
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// Kotlin
@Ann(intValue = 1, stringValue = "abc") class C
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// Kotlin
@Ann(intValue = 1, stringValue = "abc") class C
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// Java
public @interface AnnWithValue {
String value();
}
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// Java
public @interface AnnWithValue {
String value();
}
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// Kotlin
@AnnWithValue("abc") class C
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// Kotlin
@AnnWithValue("abc") class C
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Arrays as annotation parameters
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// Java
public @interface AnnWithArrayValue {
String[] value();
}
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// Java
public @interface AnnWithArrayValue {
String[] value();
}
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// Kotlin
@AnnWithArrayValue("abc", "foo", "bar") class C
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// Kotlin
@AnnWithArrayValue("abc", "foo", "bar") class C
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// Java
public @interface AnnWithArrayMethod {
String[] names();
}
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// Java
public @interface AnnWithArrayMethod {
String[] names();
}
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// Kotlin 1.2+:
@AnnWithArrayMethod(names = ["abc", "foo", "bar"])
class C
// Older Kotlin versions:
@AnnWithArrayMethod(names = arrayOf("abc", "foo", "bar"))
class D
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// Kotlin 1.2+:
@AnnWithArrayMethod(names = ["abc", "foo", "bar"])
class C
// Older Kotlin versions:
@AnnWithArrayMethod(names = arrayOf("abc", "foo", "bar"))
class D
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Accessing properties of an annotation instance
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// Java
public @interface Ann {
int value();
}
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// Java
public @interface Ann {
int value();
}
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// Kotlin
fun foo(ann: Ann) {
val i = ann.value
}
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// Kotlin
func foo(ann: Ann) {
let i = ann.value
}
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