Don’t abuse Kotlin’s scope functions

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Scope functions

Kotlin’s standard library contains several functions whose sole purpose is to execute a block of code within the context of an object.

When you call such a function on an object with a lambda expression provided, it forms a temporary scope.

M𝐚𝐤𝐞 𝐬𝐮𝐫𝐞 𝐰𝐡𝐞𝐧 𝐲𝐨𝐮 𝐮𝐬𝐞 𝐊𝐨𝐭𝐥𝐢𝐧’𝐬 𝐬𝐜𝐨𝐩𝐞 𝐟𝐮𝐧𝐜𝐭𝐢𝐨𝐧𝐬 𝐲𝐨𝐮 𝐮𝐧𝐝𝐞𝐫𝐬𝐭𝐚𝐧𝐝

• What each of those functions does
• How receiver accessible within the function’s scope [it, this]
• What they return

https://kotlinlang.org/docs/scope-functions.html

Accessing nullable properties

• Let say we have a property called binding in our fragment which is nullable

private var binding: FragmentBlankBinding? = null

How we can access this property in our code in a null-safe manner

• with : If you have a lot of properties you will end up using ? everywhere in with’s block

with(binding) {
    this?.root?.isVisible = true
}

How we can improve this :

1. let : Although now you are null-safe and you don’t need to repeat ? but you need to use it to access any property of the receiver 😬

binding?.let {
    it.root.isVisible = true
}

2. run : I prefer using this over all the other options because it’s null-safe and concise

Here you can access the properties of the receiver without repeating this everywhere

binding?.run {
    root.isVisible = true
}

Creating objects

• Many developers writing code in Kotlin but they follow Java’s coding style

val intent = Intent()
intent.putExtra("Key", "value")
intent.putExtra("Key1", "value")

How we can improve 👆 this code to make sure it’s concise and Kotlin friendly:

• let : returns the result of thelambda

val intent = Intent().let {
    it.putExtra("Key", "value")
    it.putExtra("Key1", "value")
    it.action = "CUSTOM_APP_ACTION" // Unit
}
// here intent's type will be Unit 🥵
// you can fix this by moving/removing last statement
val intent = Intent().let {
    it.putExtra("Key", "value")
    it.action = "CUSTOM_APP_ACTION"
    it.putExtra("Key1", "value") // Intent ✅
}

• apply : returns its receiver

val intent = Intent().apply {
    putExtra("Key", "value")
    putExtra("Key1", "value")
    action = "CUSTOM_APP_ACTION"
}
// here intent's type will be Intent ✅

When to use

with, let, apply, also, run

• If the property is nullable, you can use let or run

val supportedJVM: String? = null
supportedJVM?.run {receiver is avialble using this keyword
   // Lambda result will be the return value
}

supportedJVM?.let { receiver is avialble using it keyword
  // Lambda result will be the return value
}

• If the property is non-nullable, you can use with

with(languageName) { receiver is avialble using this keyword
    
    // Lambda result will be the return value
}

• You can use also when you want to do something additional work with an object orresult of some other function or expression e.g.

var formattedPrice = ""
val price = 10.plus(5).also { receiver is avialble using it keyword
    
    formattedPrice = "Price is ${it * 2}"
  
    // Context object will be the return value
}

😊😊 👏👏👏👏 HAPPY CODING 👏👏👏👏 😊😊

References

Scope functions | Kotlin

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