Kotlin Inline + Extension Function

GenericBodyExecutor to execute a given body in Kotlin by handling exception.


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Kotlin Inline + Extension Function

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What is Kotlin Extension Functions?

Kotlin provides the ability to extend a class with new functionality without having to inherit from the class or use design patterns such as Decorator. This is done via special declarations called extensions.

For example, you can write new functions for a class from a third-party library that you can't modify. Such functions can be called in the usual way, as if they were methods of the original class. This mechanism is called an extension function. There are also extension properties that let you define new properties for existing classes.

What is Kotlin Inline Functions:

An Inline function is a kind of function that is declared with the keyword inline just before the function declaration. Once a function is declared inline, the compiler does not allocate any memory for this function, instead the compiler copies the piece of code virtually at the calling place at runtime.

Let's talk about our extension function called executeBodyOrReturnNull().

inline fun <T> executeBodyOrReturnNull(crossinline body: () -> T): T? {
    return try {
    } catch (e: Exception) {

In every Android project, we have to deal with Exception by using TryCatch blocks. Writing too many TryCatch is a bad approach in terms of Modern Application Development using Kotlin. For this we can use an extension function that take a body as a parameter to execute the given block and if any exception occur, function print the StackTrace return anull object. Also, we are using the another superpower of Kotlin called Inline functions.

Let's take a look at the usages:

data class GenericData(val data: String)

We have a Data Class called GenericData which take data : String as a parameter. But in our app, we might need to cast the data : String to something else, like Int or Double.

If, we directly cast data : String into something else, program might throw Exception if something goes wrong. So, how can we solve this problem?

Simply, we can call our extension function executeBodyOrReturnNull().

val firstObject = executeBodyOrReturnNull<Int> { GenericData("0").data.toInt() }

val secondObject = executeBodyOrReturnNull<Int> { GenericData("Hello").data.toInt() }

If, we run the code, the result would be:


and the StackTrace is

java.lang.NumberFormatException: For input string: "Hello"
    at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:67)
    at java.base/java.lang.Integer.parseInt(Integer.java:668)
    at java.base/java.lang.Integer.parseInt(Integer.java:786)
    at GenericBodyExecutor$Companion.main(GenericBodyExecutor.kt:7)
    at GenericBodyExecutor.main(GenericBodyExecutor.kt)

Casting "0" into Int is successful, but casting "Hello" into Int will throw NumberFormatException, hence executeBodyOrReturnNull() returning null object.

Full implementation:

Happy Coding...

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