Is there way to add one more argument to the function(which has var args) with default value without breaking existing calls?

Question

I have a function

fun foo(
    id: String,
    vararg values: Int,
){
  ...    
}

and there are calls like these

fun bar1(){
    foo("id_1")
    foo("id_2", 1)
    foo("id_3", 1, 2, 3)
}

Now I've understood that I need to add one more argument to foo. but I don't want to break existing calls so I tried to add it with default values:

fun foo(
    id: String,
    attributes: Array<String> = arrayOf("a", "b"),
    vararg values: Int,
){
  ...
}

But

foo("id_2", 1)
foo("id_3", 1, 2, 3)

became broken.

Is there way to add one more argument with default value without breaking existing calls ?

gstackoverflow · Accepted Answer · 2024-11-02 09:03:08Z

Option 1:

You can, if you move the new parameter to the end:

fun foo(
    id: String,
    vararg values: Int,
    attributes: Array<String> = arrayOf("a", "b"),
) {
    // ...
}

But it becomes a bit awkward to call:

fun bar1() {
    foo("id_1")
    foo("id_2", 1)
    foo("id_3", 1, 2, 3)
    foo("id_3", 1, 2, 3, attributes = arrayOf("a", "b"))
}

You need to specify the parameter name, otherwise the compiler will think the array is still part of the varargs parameter.

Option 2:

You can overload the function:

fun foo(
    id: String,
    vararg values: Int,
) {
    foo(id, arrayOf("a", "b"), *values)
}

fun foo(
    id: String,
    attributes: Array<String>,
    vararg values: Int,
) {
    // ...
}

Then you can call it like this:

fun bar1() {
    foo("id_1")
    foo("id_2", 1)
    foo("id_3", 1, 2, 3)
    foo("id_3", arrayOf("a", "b"), 1, 2, 3)
}

This is more elegant at the call site but you have a little overhead at the declaration side.

redoc · Accepted Answer · 2024-11-02 08:50:02Z

1

I am new to kotlin but you made me learn this today, thanks! was using kotlin playground..

You were asking about way to add one more argument with default value without breaking existing calls.

You can do this by using attributes after vararg like

fun foo(
    id: String,
    vararg values: Int,
    attributes: Array<String> = arrayOf("a", "b"),
){
  ...
}

But wait, that will raise error regarding type, because the attribute which you meant to convey at last of foo() will also be considered as vararg, so to use this code we will have to call the function like:

foo("id_3", 1, 2, 3,attributes=loremipsum)

wherever required you can add ,attributes=loremipsum and if not leave it.

answered Nov 2, 2024 at 8:50

redoc

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1 Comment

gstackoverflow Over a year ago

so there is not nice way to do it....

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