# Dynamically invoke Function\ **URL:** \ **Category:** Support\ **Created:** [April 20, 2020, 9:02pm UTC](https://discuss.kotlinlang.org/t/dynamically-invoke-function-r/17242 "2020-04-20T21:02:07Z")\ **Posts on this page:** 6\ **Page:** 1

**Author:** ![sugarmanz](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/sugarmanz/32/7445_2.png) [@sugarmanz](https://discuss.kotlinlang.org/u/sugarmanz)\ **Post date:** [April 20, 2020, 9:02pm UTC](https://discuss.kotlinlang.org/t/dynamically-invoke-function-r/17242/1 "2020-04-20T21:02:07Z")

I’m building a utility to translate lambdas into callable references inside a different language context. Essentially, making Kotlin lambdas callable from a V8 runtime living in the JVM. I have a method that takes a Function and I would like to invoke it. From what I’m understanding, it looks like I have to do something like this in order to support any lambda: ``` fun Function.call(vararg args: Any?): R = when (args.size) { 0 -> (this as Function0).invoke() 1 -> (this as Function1).invoke(args[0]) 2 -> (this as Function2).invoke(args[0], args[1]) 3 -> (this as Function3).invoke(args[0], args[1], args[2]) 4 -> (this as Function4).invoke(args[0], args[1], args[2], args[3]) 5 -> (this as Function5).invoke(args[0], args[1], args[2], args[3], args[4]) 6 -> (this as Function6).invoke(args[0], args[1], args[2], args[3], args[4], args[5]) 7 -> (this as Function7).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6]) 8 -> (this as Function8).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7]) 9 -> (this as Function9).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8]) 10 -> (this as Function10).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9]) 11 -> (this as Function11).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10]) 12 -> (this as Function12).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11]) 13 -> (this as Function13).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12]) 14 -> (this as Function14).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13]) 15 -> (this as Function15).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13], args[14]) 16 -> (this as Function16).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13], args[14], args[15]) 17 -> (this as Function17).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13], args[14], args[15], args[16]) 18 -> (this as Function18).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13], args[14], args[15], args[16], args[17]) 19 -> (this as Function19).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13], args[14], args[15], args[16], args[17], args[18]) 20 -> (this as Function20).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13], args[14], args[15], args[16], args[17], args[18], args[19]) 21 -> (this as Function21).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13], args[14], args[15], args[16], args[17], args[18], args[19], args[20]) 22 -> (this as Function22).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13], args[14], args[15], args[16], args[17], args[18], args[19], args[20], args[21]) else -> (this as FunctionN).invoke(*args) } ``` Originally, I found these [specifications](https://github.com/JetBrains/kotlin/blob/master/spec-docs/function-types.md#arity-and-invocation-with-vararg) regarding invoking functions and it looked super promising, but it seems those docs are outdated and no longer represent the current state. I tried looking for the equivalent in the current docs, but to no avail. Additionally, I was also considering checking arity against the length of the arguments, but arity is contained in the FunctionBase interface and since that is in `kotlin.jvm.internal`, it seemed inappropriate to use. I would appreciate any confirmation on my approach or suggestions on how to proceed otherwise. Thanks! ---

**Author:** ![SackCastellon](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/sackcastellon/32/4553_2.png) [@SackCastellon](https://discuss.kotlinlang.org/u/SackCastellon)\ **Post date:** [April 20, 2020, 11:29pm UTC](https://discuss.kotlinlang.org/t/dynamically-invoke-function-r/17242/2 "2020-04-20T23:29:06Z")

> [@sugarmanz](#): > > ```auto > fun Function.call(vararg args: Any?): R = when (args.size) { > 0 -> (this as Function0).invoke() > 1 -> (this as Function1).invoke(args[0]) > 2 -> (this as Function2).invoke(args[0], args[1]) > 3 -> (this as Function3).invoke(args[0], args[1], args[2]) > 4 -> (this as Function4).invoke(args[0], args[1], args[2], args[3]) > 5 -> (this as Function5).invoke(args[0], args[1], args[2], args[3], args[4]) > 6 -> (this as Function6).invoke(args[0], args[1], args[2], args[3], args[4], args[5]) > 7 -> (this as Function7).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6]) > 8 -> (this as Function8).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7]) > 9 -> (this as Function9).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8]) > 10 -> (this as Function10).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9]) > 11 -> (this as Function11).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10]) > 12 -> (this as Function12).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11]) > 13 -> (this as Function13).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12]) > 14 -> (this as Function14).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13]) > 15 -> (this as Function15).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13], args[14]) > 16 -> (this as Function16).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13], args[14], args[15]) > 17 -> (this as Function17).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13], args[14], args[15], args[16]) > 18 -> (this as Function18).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13], args[14], args[15], args[16], args[17]) > 19 -> (this as Function19).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13], args[14], args[15], args[16], args[17], args[18]) > 20 -> (this as Function20).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13], args[14], args[15], args[16], args[17], args[18], args[19]) > 21 -> (this as Function21).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13], args[14], args[15], args[16], args[17], args[18], args[19], args[20]) > 22 -> (this as Function22).invoke(args[0], args[1], args[2], args[3], args[4], args[5], args[6], args[7], args[8], args[9], args[10], args[11], args[12], args[13], args[14], args[15], args[16], args[17], args[18], args[19], args[20], args[21]) > else -> (this as FunctionN).invoke(*args) > } > > ``` There is a function in the stdlib that does exactly this: > **[call - Kotlin Programming Language](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.reflect/-k-callable/call.html)** ---

**Author:** ![sugarmanz](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/sugarmanz/32/7445_2.png) [@sugarmanz](https://discuss.kotlinlang.org/u/sugarmanz)\ **Post date:** [April 21, 2020, 12:30am UTC](https://discuss.kotlinlang.org/t/dynamically-invoke-function-r/17242/3 "2020-04-21T00:30:47Z")

Thanks for the quick reply! I am aware of that method, because I’m using it for member functions on a class. I wasn’t sure how to get a KCallable reference from a Lambda type. Trying to use reflection on the Lambda types result in the following error: > This class is an internal synthetic class generated by the Kotlin compiler, such as an anonymous class for a lambda, a SAM wrapper, a callable reference, etc. It’s not a Kotlin class or interface, so the reflection library has no idea what declarations does it have. Please use Java reflection to inspect this class: class com.example$testExample$1$function$1 EDIT: Just found this: ``` value.reflect().call("arg1", "arg2", ...) ``` But there is still an error: > Introspecting local functions, lambdas, anonymous functions and local variables is not yet fully supported in Kotlin reflection EDIT 2: Which makes sense given the [docs](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.reflect.jvm/reflect.html#reflect) I just found on it. ---

**Author:** ![nickallendev](https://avatars.discourse-cdn.com/v4/letter/n/cdc98d/32.png) [@nickallendev](https://discuss.kotlinlang.org/u/nickallendev)\ **Post date:** [April 21, 2020, 3:27am UTC](https://discuss.kotlinlang.org/t/dynamically-invoke-function-r/17242/4 "2020-04-21T03:27:35Z")

You can also use JVM reflection to call methods. ---

**Author:** ![sugarmanz](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/sugarmanz/32/7445_2.png) [@sugarmanz](https://discuss.kotlinlang.org/u/sugarmanz)\ **Post date:** [April 21, 2020, 4:22am UTC](https://discuss.kotlinlang.org/t/dynamically-invoke-function-r/17242/5 "2020-04-21T04:22:10Z")

Gotcha. Just for clarities sake, this seems to work fine: ``` lambdaFunction::class.java.methods.find { it.name == "invoke" }.invoke(value, "arg1", "arg2", ...) ``` Though, I would love to just handle this as a KCallable, but it seems that I’ll have to wait for that. I appreciate the help and direction here. Thanks! ---

**Author:** ![emilesteenkamp](https://avatars.discourse-cdn.com/v4/letter/e/f07891/32.png) [@emilesteenkamp](https://discuss.kotlinlang.org/u/emilesteenkamp)\ **Post date:** [January 26, 2024, 10:27pm UTC](https://discuss.kotlinlang.org/t/dynamically-invoke-function-r/17242/6 "2024-01-26T22:27:00Z")

What should you pass as the `value`? I am trying to do the exact same thing, however my lambda function is not defined within any class. While debugging I can see that the declaring class required for my Lambda function invocation is of type `KFunctionImpl`, but it is not clear where this class is coming from and how to pass it into the invocation