Kotlin functional way - kotlin

Question

I'm trying to perfect myself in Kotlin with functional programming. And then I did this:
I was tired of the way I write try - catch, and created the following function:
package com.learning.functionalway
fun <T> tryCatch(t: T?, excpetion: (Throwable)): T? = try {
t
} catch (e: Exception) {
throw excpetion
}
And I used it like this:
#Service
class ProductService(val repository: IProductRepository, val repositoryS: IStockRepository) : IService<Product, ProductModel> {
override fun find(id: Long) = tryCatch(
repository.find(id),
DataNotFound("Product not found"))
other methods ..
}
And my exception that I deal in the "Exception Handler"
class DataNotFound(message: String?) : Exception(message) {
}
Is this a correct way I used to modify the way I use try - catch?
Or are there better ways to do it?

Answer 1

Your solution is not a "more functional" way of doing error handling but rather just arguably a slight improvement in try-catch syntax.
If you truly want to embrace functional programming, I'd recommend you to check out Arrow. The standard Kotlin library is not enough for advanced functional programming concepts (such as error handling) and Arrow fills that gap.
You can read their documentation on how to do proper error handling.
If you fancy a talk about it, I'd recommend you to check out this video (topic of error handling starts here) which is about Kotlin and functional programming.

Answer 2

One way to remake the try-catch syntax to make it more functional is like this:
sealed class Try<out Output> {
class Some<Output>(val output: Output) : Try<Output>()
class None(val exception: Exception) : Try<Nothing>()
companion object {
operator fun <Output> invoke(toTry: () -> Output) = try {
Some(toTry())
} catch (e: Exception) {
None(e)
}
}
val value get() = when(this) {
is Some -> output
is None -> null
}
infix fun catch(onException: (Exception) -> Unit): Output? = when (this) {
is Some -> output
is None -> {
onException(exception)
null
}
}
}
class ProductService(val repository: IProductRepository, val repositoryS: IStockRepository) : IService<Product, ProductModel> {
override fun find(id: Long): Product? = Try {
repository.find(id)
} catch { exception ->
println("Error trying to get product $exception")
}
//other methods ..
}
The key advantage here is that unlike in the original syntax you can do things by parts. So if you have a lot of tries to do and want to handle all the results at the end, with this syntax you can.