Sure, maybe some form of intersection types will let this compile, or an annotation or whatever. In this case T : Any? from the function signature, meaning it won't compile because the signature for lookup can't be inferred, not even in the null !is T branch (there's no smart cast to T : Any). The type of T::class is not KClass, it's KClass, and the java extension property preserves the nullability. If you think about it, T::class.java isn't type Class. (TIL null is T is valid for reified type parameters.) call-site: val d = deserializer() // d is Deserializer val d1 = deserializer() // d1 is Deserializer, which is a wrapper over a Deserializer Inline fun deserializer(): Deserializer = if ( null is T) lookup( T:: class).optional() else lookup( T:: class) optional(): Deserializer = Deserializer() Numeric constants.Fun lookup( type : KClass): Deserializer = TODO()įun Deserializer. The example demonstrates the declaration and use of nullable variables of different types. If a variable is declared as a nullable variable, then it can be assigned the null value. Type – any basic type of the Kotlin language ( Int, Double, Byte, Short, UByte, Char, String and others).This is done by adding the symbol ? (question mark) to type name Type? Unlike the Java language (as well as other languages), Kotlin allows the programmer to directly specify nullable types. Declaration of variables that support null-value (nullable-variables). This is a significant advantage of the Kotlin language. That is, the error can be immediately identified and corrected, otherwise the program code will not be compiled. In the Kotlin language, the type system is organized in such a way that errors using nullable types are already detected at compile time. As a consequence, an exception is thrown (in Java it is a ), which is a consequence of the fact that the compiler was unable to detect an error during the compilation of the program. In other programming languages (Java in particular), incorrect use of nullable elements leads to run-time errors, which is very undesirable. nullableString string // This will work however PDF - Download Kotlin for. When writing programs, it is important to use nullable elements correctly to avoid errors. To make them able to hold null values, you have to explicitly denote that by putting a behind them: String var string : String 'Hello World' var nullableString: String null string nullableString // Compiler error: Can't assign nullable to non-nullable type. non-nullable – elements that cannot take a null value.nullable are elements that can take a null value Nullable types are a feature of some programming languages which allow a value to be set to the special value NULL instead of the usual possible values of.Based on this context, Kotlin language elements are divided into two types:
In the Kotlin language, null means that there is no value for variables declared as val or var at the moment. The terms null-value and zero-value are different things.
In modern programming languages (including Java, C#, etc.) there are situations when a value does not contain any value.
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