Kotlin 1.0.0 Beta Candidate

Language

• Imports from objects
• @Deprecated supports ERROR and HIDDEN levels (@HiddenDeclaration is deprecated)
• Smart casts for captured local var's that are not modified in lambdas
• Single-file classes can have many main()'s
• internal visibility checked in the compiler
• No defensive copying needed for varargs
• All Java methods with matching signatures are operators
• Rename: unaryMinus/unaryPlus for unary operators
• Rename: getValue/setValue for delegated properties
• Checks for operator signatures at declarations sites
• infix modifier for infix functions
• Rename sparam annotation target to setparam
• @UnsafeVariance annotation
• fun foo<T>() deprecated in favor of fun <T> foo()
• Constraints on type parameters should occur either in where or in <…>
• x is Array<Foo> forbidden in favor of x is Array<*> && x.isArrayOf<Foo>()
• Callable references restricted to support bound references later
• PropertyMetadata deprecated in favor of KProperty<*>
• if with no else in expression position is an error
• Letters and digits right before/after string and char literals are prohibited
• invoke convention for extension functions is removed
• Visibility requirements for members
• Protected members in objects are prohibited
• final in interfaces is prohibited
• Visibility for local classes is prohibited
• Local interfaces are prohibited
• Private setters for non-private lateinit vars are prohibited
• Nothing-returning functions must declare return type explicitly
• Annotations on multi-declarations are prohibited
• Checks for escaped identifiers (backticks) to conform to JVM requirements
• Supertypes of the form T.() -> Foo are prohibited
• Foo<Int>.Bar is prohibited
• Type parameters for properties are prohibited unless they are used in the receiver type
• Parameter annotations and default values in function types are prohibited
• inline properties are prohibited
• ;; is reserved for future use

Libraries

• Formerly deprecated declarations have been dropped
• size(), length() etc are made properties
• List.remove(int) is renamed to removeAt
• Collection<E>.contains(Any?), Map<K, V>.get(Any?) and other similar function are now type-safe: contains(E), get(K)
• containsRaw, getRaw extensions and alike are defined for the Java-like utyped behavior
• Regex API changes: matchEntire added, match/matchAll renamed to find/findAll, also regex in string can be used isntead of regex.hasMatch(string)
• listOf() doesn't make a defensive copy
• StringBuilder {} function deprecated in favor of buildString {}
• Rename: merge -> zip, join removed (use joinToString), mapNotNull deprecated to be changed later

Java interop

• Java classes inherit static from supertypes
• List<Nothing> is compiled to raw List to facilitate subtyping in Java
• Support "static overrides" for Java fields
• Top-level privates are private to file
• Names of internal functions and properties are mangled
• Kotlin classes see inherited statics and members of inherited companion objects
• @Synchronized and @Volatile are inapplicable to unimplemented functions
• isFoo() instead of getIsFoo() for properties named isFoo
• Old package facades are dropped
• Inheritance rules comply with Java 8
• is distinguishes MutableList from List and supports functions of different arities
• Int, String and other basic types are Serializable
• @JvmField is required to make something a field
• INSTANCE for objects (instead of INSTANCE$)
• Constant pool stings are resued to reduce metadata sizes
• @KotlinSignature is deprecated
• Java sees defaul implementations of methods in the interface Foo as statics in Foo.DefaultImpls class
• Constants from Java libraries are inlined into Kotlin byte code
• @publicField is deprecated

Tools

• Compiler daemon enabled by default in the IDE
• Parallel Compilation of Independent Modules in the daemon mode
• External annotations support removed

IDE

• Parameter Info everywhere
• Completion for callable references after ::
• Actions to generated equals()/hashCode()
• Actions to generate secondary constructors
• '*'-imports configuration
• Unit-testing support