If you have a valid reified type parameter T then you can use:

obj  is  T  
obj !is  T
obj  as  T  
Obj  as? T

and reflection.

The way that it works is that the type parameter is replaced by the actual type when the inline code is generated.

So at the calling site:

IS <Int>(23)

becomes:

obj is Int

which is perfectly valid and works.

Type reification is a small step in the right direction but you have to admit that Kotlin is boxed in by what Java and the JVM allows it to do. However, Java compatibility is well worth the trade off.

Summary

• You can store a reference to an anonymous function in a variable or pass the function as an argument to another function.

• You can store a reference to a named function in a variable or parameter using the reflection reference operator ::

• A reference to a lambda function can also be stored in a variable or passed as a parameter.

• A lambda is defined as { parameter list -> code }

• A lambda, anonymous or named function can be used as extension functions.

• The shortened forms that you can use to define and call functions make them very suitable to implement DSLs and metaprogramming.

• You cannot have a return in a lambda but you can use a qualified return.

• Lambdas can be simplified to the point where they are difficult to understand. You can use it as a default parameter of a single parameter lambda, leave out parameters using underscore, and execute a lambda immediately.

• All Kotlin functions support closure where variables that were in scope at the time the function was created remain accessible to the function even after they have gone out of scope.

• Inline functions can be used to improve performance and add features such as non-local returns and reification

This article is an extract from: 

Programmer's Guide To Kotlin Third Edition

You can buy it from: Amazon

Contents

1. What makes Kotlin Special
2. The Basics:Variables,Primitive Types and Functions 
3. Control
        Extract: If and When 
4. Strings and Arrays
5. The Class & The Object ***NEW!
6. Inheritance
7. The Type Hierarchy
   
8. Generics
9. Collections, Iterators, Sequences & Ranges
       Extract: Iterators & Sequences 
10. Advanced functions 
11. Anonymous, Lamdas & Inline Functions
    
12. Data classes, enums and destructuring
        Extract: Destructuring 
13. Exceptions, Annotations & Reflection
14. Coroutines
        Extract: Coroutines 
15. Working with Java
        Extract: Using Swing
16. Compose Multiplatform
        Extract: Compose Layout 

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