# Mutable Function Parameters

**URL:** <https://discuss.kotlinlang.org/t/mutable-function-parameters/3758>\
**Category:** Language Design\
**Created:** [July 15, 2017, 11:59am UTC](https://discuss.kotlinlang.org/t/mutable-function-parameters/3758 "2017-07-15T11:59:58Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![ahmadalsharif.dev](https://avatars.discourse-cdn.com/v4/letter/a/bbe5ce/32.png) [@ahmadalsharif.dev](https://discuss.kotlinlang.org/u/ahmadalsharif.dev)\
**Post date:** [July 15, 2017, 11:59am UTC](https://discuss.kotlinlang.org/t/mutable-function-parameters/3758/1 "2017-07-15T11:59:58Z")

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Hey everyone,

I was just thinking why can’t we optionally (and without any modifiers they are val) have mutable function parameters like:

```
fun (var convertView: View?) {
    if (convertView == null) convertView = View(activity)
    // do something with convertView
}

```

---

<div class="post-metadata">

**Author:** ![elizarov](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/elizarov/32/2164_2.png) [@elizarov](https://discuss.kotlinlang.org/u/elizarov)\
**Post date:** [July 18, 2017, 4:02pm UTC](https://discuss.kotlinlang.org/t/mutable-function-parameters/3758/2 "2017-07-18T16:02:39Z")

</div>

This was discussed here: [Function parameters are "val" not "var"?](https://discuss.kotlinlang.org/t/function-parameters-are-val-not-var/897/)  
The rationale for this behavior is explained here in “Parameters are Immutable” section: [Kotlin M5.1 | The Kotlin Blog](https://blog.jetbrains.com/kotlin/2013/02/kotlin-m5-1/)