Kotlin 2.1: Language Updates

Transcript

1. Kotlin 2.1 Language Updates
3. Language Features •Suppor t for requiring opt-in to extend APIs •Non-local break and continue •Multi-dollar interpolation •Guard conditions in when-with-subject expressions •Improved exhaustiveness checks for when expressions with sealed classes
4. Opt-in requirements for subclasses
5. Opt-in requirements for subclasses @RequiresOptIn( level = RequiresOptIn.Level.ERROR, message = "Interfaces in this library are experimental" ) annotation class UnstableApi() @SubclassOptInRequired(UnstableApi :: class) interface CoreLibraryApi interface MyImplementation : CoreLibraryApi Library User code
6. Opt-in requirements for subclasses @RequiresOptIn( level = RequiresOptIn.Level.ERROR, message = "Interfaces in this library are experimental" ) annotation class UnstableApi() @SubclassOptInRequired(UnstableApi :: class) interface CoreLibraryApi interface MyImplementation : CoreLibraryApi Library User code
7. Opt-in requirements for subclasses @RequiresOptIn( level = RequiresOptIn.Level.ERROR, message = "Interfaces in this library are experimental" ) annotation class UnstableApi() @SubclassOptInRequired(UnstableApi :: class) interface CoreLibraryApi @OptIn(UnstableApi :: class) interface MyImplementation : CoreLibraryApi Library User code
8. Local break and continue in lambdas
9. Local break and continue in lambdas fun List<File>.readFirstLines(): List<String> = buildList { for (file in this@readFirstLines) { val reader = file.bufferedReader(Charsets.UTF_8) val line = reader.readLine() if (line.isNullOrEmpty()) continue else add(line) } } "Read the first line from each file in the list"
10. Local break and continue in lambdas fun List<File>.readFirstLines(): List<String> = buildList { for (file in this@readFirstLines) { val reader = file.bufferedReader(Charsets.UTF_8) val line = reader.readLine() if (line.isNullOrEmpty()) continue else add(line) } }
11. Local break and continue in lambdas fun List<File>.readFirstLines(): List<String> = buildList { for (file in this@readFirstLines) { val reader = file.bufferedReader(Charsets.UTF_8) val line = reader.readLine() if (line.isNullOrEmpty()) continue else add(line) } }
12. Local break and continue in lambdas fun List<File>.readFirstLines(): List<String> = buildList { for (file in this@readFirstLines) { val reader = file.bufferedReader(Charsets.UTF_8) val line = reader.readLine() if (line.isNullOrEmpty()) continue else add(line) } }
13. Local break and continue in lambdas fun List<File>.readFirstLines(): List<String> = buildList { for (file in this@readFirstLines) { val reader = file.bufferedReader(Charsets.UTF_8) val line = reader.readLine() if (line.isNullOrEmpty()) continue else add(line) } } Realize, that we need to use the resources properly
14. Local break and continue in lambdas fun List<File>.readFirstLines(): List<String> = buildList { for (file in this@readFirstLines) { file.bufferedReader(Charsets.UTF_8).use { reader -> val line = reader.readLine() // this is now a 'continue' inside a lambda if (line.isNullOrEmpty()) continue else add(line) } } }
15. Local break and continue in lambdas fun List<File>.readFirstLines(): List<String> = buildList { for (file in this@readFirstLines) { file.bufferedReader(Charsets.UTF_8).use { reader -> val line = reader.readLine() // this is now a 'continue' inside a lambda if (line.isNullOrEmpty()) continue else add(line) } } }
16. Local break and continue in lambdas fun List<File>.readFirstLines(): List<String> = buildList { for (file in this@readFirstLines) { file.bufferedReader(Charsets.UTF_8).use { reader -> val line = reader.readLine() // this is now a 'continue' inside a lambda if (line.isNullOrEmpty()) continue else add(line) } } } -Xnon-local-break-continue
17. Multi-dollar interpolation
18. Multi-dollar interpolation val jsonSchema: String = """ { "$id": "https: // example.com/product.schema.json", }"""
19. Multi-dollar interpolation val jsonSchema: String = """ { "$id": "https: // example.com/product.schema.json", }""" Interpolation fails for "id"
20. Multi-dollar interpolation val jsonSchema: String = """ { "${'$'}id": "https: // example.com/product.schema.json", }""" A workaround
21. Multi-dollar interpolation val jsonSchema: String = $$""" { "$id": "https: // example.com/product.schema.json", }""" -Xmulti-dollar-interpolation Use $$ as a symbol sequence for interpolation
22. Multi-dollar interpolation val jsonSchema: String = $$""" { "$id": "https: // example.com/product.schema.json", "parameter": $$parameter" }""" val parameter = "value" Use $$ as a symbol sequence for interpolation
23. Multi-dollar interpolation val jsonSchema: String = $$$$$$$$$$$$$$$$$$$$$$""" { "$id": "https: // example.com/product.schema.json", "parameter": $$$$$$$$$$$$$$$$$$$$$$parameter" }""" val parameter = "value" :)
26. Guard conditions in when-with-subject expressions
27. when { order is YearlySubscription && order.amount > 100 -> applyDiscount(order) order is MonthlySubscription -> startSubscription(order) order is OneTimeOrder -> processOrder(order) } val order = getOrder() Guard conditions in when-with-subject expressions
28. when { order is YearlySubscription && order.amount > 100 -> applyDiscount(order) order is MonthlySubscription -> startSubscription(order) order is OneTimeOrder -> processOrder(order) } val order = getOrder() Potentially a logical error Repetition is not nice Guard conditions in when-with-subject expressions
29. when { order is YearlySubscription && order.amount > 100 -> applyDiscount(order) order is YearlySubscription -> processSubscription(order) order is MonthlySubscription -> startSubscription(order) order is OneTimeOrder -> processOrder(order) } val order = getOrder() Guard conditions in when-with-subject expressions
30. when(order) { is YearlySubscription && order.amount > 100 -> applyDiscount(order) is YearlySubscription -> processSubscription(order) is MonthlySubscription -> startSubscription(order) is OneTimeOrder -> processOrder(order) } val order = getOrder() Guard conditions in when-with-subject expressions
31. when(order) { is YearlySubscription && order.amount > 100 -> applyDiscount(order) is YearlySubscription -> processSubscription(order) is MonthlySubscription -> startSubscription(order) is OneTimeOrder -> processOrder(order) } val order = getOrder() Error: expecting ' -> ' && Guard conditions in when-with-subject expressions
32. when(order) { is YearlySubscription && order.amount > 100 -> applyDiscount(order) is YearlySubscription -> processSubscription(order) is MonthlySubscription -> startSubscription(order) is OneTimeOrder -> processOrder(order) } val order = getOrder() if Guard conditions in when-with-subject expressions Guarded conditions: KEEP - 371
33. when(order) { is YearlySubscription if order.amount > 100 -> applyDiscount(order) is YearlySubscription -> processSubscription(order) is MonthlySubscription -> startSubscription(order) is OneTimeOrder -> processOrder(order) } val order = getOrder() Guard conditions in when-with-subject expressions
34. when(order) { is YearlySubscription -> processSubscription(order) is YearlySubscription if order.amount > 100 -> applyDiscount(order) is MonthlySubscription -> startSubscription(order) is OneTimeOrder -> processOrder(order) } val order = getOrder() The 'when' branch is never reachable Guard conditions in when-with-subject expressions
35. when(order) { is YearlySubscription if order.amount > 100 -> applyDiscount(order) is YearlySubscription -> processSubscription(order) is MonthlySubscription -> startSubscription(order) is OneTimeOrder -> processOrder(order) } val order = getOrder() Guard conditions in when-with-subject expressions
37. Improved exhaustiveness checks for when expressions with sealed classes sealed class Result object Error: Result() class Success(val value: String): Result() fun <T : Result> render(result: T) = when (result) { Error -> "Error!" is Success -> result.value // Requires no else branch } Required else branch before 2.1
38. Change of JSpecify nullability mismatch diagnostics severity to 'strict'
39. Change of JSpecify nullability mismatch diagnostics severity to 'strict' import org.jspecify.annotations.*; public class SomeJavaClass { @NonNull public String foo() { ... } @Nullable public String bar() { ... } } Java
40. Change of JSpecify nullability mismatch diagnostics severity to 'strict' import org.jspecify.annotations.*; public class SomeJavaClass { @NonNull public String foo() { ... } @Nullable public String bar() { ... } } Java Kotlin val sjc = SomeJavaClass() sjc.foo().length sjc.bar().length
41. Change of JSpecify nullability mismatch diagnostics severity to 'strict' import org.jspecify.annotations.*; public class SomeJavaClass { @NonNull public String foo() { ... } @Nullable public String bar() { ... } } Java Kotlin val sjc = SomeJavaClass() sjc.foo().length sjc.bar().length
42. Change of JSpecify nullability mismatch diagnostics severity to 'strict' import org.jspecify.annotations.*; public class SomeJavaClass { @NonNull public String foo() { ... } @Nullable public String bar() { ... } } Java Kotlin val sjc = SomeJavaClass() sjc.foo().length sjc.bar() ?. length Raises an error in the default strict mode because the result is nullable. To avoid the error, use ?.length instead
43. Change of JSpecify nullability mismatch diagnostics severity to 'strict' import org.jspecify.annotations.*; public class SomeJavaClass { @NonNull public String foo() { ... } @Nullable public String bar() { ... } } Java Kotlin val sjc = SomeJavaClass() sjc.foo().length sjc.bar() ?. length kotlin { compilerOptions { freeCompilerArgs.add(" -- Xnullability-annotations=strict") } } // gradle.build.kts / / ignore | warning | strict
44. https://kotlinlang.org