Hi, how do we pass the string parameter 'emessage' to the exception instance ```fun String?.throwO...

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[althaf]

Hi, how do we pass the string parameter 'emessage' to the exception instance

fun String?.throwOnEmptyOrNull(emessage: String, exceptionClass: Class<out Exception>): String {
    return this.takeIf { !it.isNullOrBlank() } ?: throw exceptionClass.newInstance()
}

val ss : String? = null
println("test 1 ${ss.throwOnEmptyOrNull("roles can't be empty or not", IllegalArgumentException::class.java)}")

This is working for me, however i'm stuck at passing the message to exception

[diesieben07]

You should really consider passing in a factory function instead of relying on classes and reflection.
However if you must, you have to use getConstructor(String::class.java) and then call newInstance on the constructor (this is using Java reflection).

[althaf]

@diesieben07 i'm really new writting factory function, i know it something like this

fun <T>String?.throwOnEmptyOrNull(emessage: String, exceptionClass: T): String {
    return this.takeIf { !it.isNullOrBlank() } ?: throw exceptionClass.newInstance()
}

however i dont know the full syntax to complete this with constructor call

[diesieben07]

fun String?.throwOnEmptyOrNull(emessage: String, exceptionFactory: (String) -> Throwable): String {
    return this.takeIf { !it.isNullOrBlank() } ?: throw exceptionFactory(emessage)
}

// usage:
"hello".throwOnEmptyOrNull("should not be empty", ::IllegalArgumentException)

[ephemient]

built-in require/requireNotNull throw IllegalArgumentException:

require(!ss.isNullOrEmpty()) { "roles can't be empty or not" }

[ephemient]

also they work with smart casting (using contacts) and your function doesn't

[diesieben07]

True, I should have chosen a different example

[ephemient]

to match the original example,

println("test 1 ${requireNotNull(ss?.ifEmpty { null }) { "roles can't be empty or not" }}")

[diesieben07]

But that does not have the ability to pass in a custom exception class

[althaf]

@diesieben07 thank you that worked like a charm. However, i'm yet to understand how it works. What is the key word that i have to search to learn more about this feature ?

[althaf]

@ephemient thank you for your support as well

[diesieben07]

https://kotlinlang.org/docs/lambdas.html

[diesieben07]

Higher order functions and lambdas

[ephemient]

::foo is a reference, of which there are several types. in this case only one single-arg constructor can match the expected type, so ::IllegalArgumentException is short for { it: String -> IllegalArgumentException(it) } (with some minor differences you don't need to worry about)

[althaf]

Thank you 🙂