What is the difference between these ways for defining functions? - kotlin

Question

I am from a background of Javascript trying to learn some Kotlin.
I know i can define my function by
fun add(a: Int , b: Int): Int{
return a+b
}
I am trying this
val add = {
a:Int,b:Int->
println("I am calculating the sale => no body you guy [$x+$y]");
//works
}
val add = { a:Int ,b : Int ->
//How do i return from this function
}
Also Is this a right way to define Kotlin functions? and Whats the difference with the first way ?

Answer 1

Also Is this a right way to define Kotlin functions? and Whats the difference with the first way ?
This is not even "a way to define Kotlin functions".
In JavaScript, all functions are reified: they are first-class values you can refer to from variables and pass around. Not so in Kotlin, just as in many other languages like Java, C++, Objective C and so on.
A function is just a declaration, you can call it but you can't otherwise directly refer to it. Separate language features allow you to create functional objects that delegate to these functions, and you can pass these objects around.
Therefore,
fun add(a: Int , b: Int): Int {
return a + b
}
is a function declaration and
val add = {a: Int, b: Int ->
a + b
}
is four things:
declaration of a variable add
declaration of an anonymous implementation of the functional type (Int, Int) -> Int
instantiation of this anonymous type, resulting in a functional object
assignment of the object to the variable add.
The object has a method invoke(a: Int, b: Int): Int whose implementation you have given in the block:
fun invoke(a: Int, b: Int): Int {
return a + b
}
You can call it explicitly:
val result = add.invoke(a, b)
and on top of that Kotlin defines syntax sugar that allows you to omit the explicit .invoke.

Answer 2

You don't need the explicit return there
val add = { a: Int, b: Int ->
a + b
}
add(2, 3) // => 5

Answer 3

Hopefully this will work.
val onChange = {
a:Int,b:Int->
println("I am calculating the sale => no body you guy [$x+$y]");
//works
}
val add = { a:Int ,b : Int ->
println("Sunm ${a+b}")
//How do i return from this function
}
Log.v("Response", add(4,3))
Output
V/Response: Sum 7

Answer 4

You can't return values in kotlin like this, it will give error of type mismatch as you havn't declared any return type :
fun add(a: Int , b: Int){
return a+b
} //wrong
we declare return type in kotlin as :
fun add(a: Int , b: Int) : Int{
return a+b
}
Secondly,
val add = { a:Int ,b : Int ->
}
this is not a function, its a declaration of value assignment
In kotlin we declare function by adding "fun" before your function name as
//you can add access modifiers(private,public,protected) if needed just before "fun"(by default its public)
fun add (){ //if it returns any value then add ": {datatype}" just right of "()"
//your code here
}
Hope it helped you :)