extension function

gistfile1.txt

Extension functions in Kotlin allow you to natively implement the "decorator" pattern. For example,
they allow you to write new functions for a class from a third-party library that you can't modify. 
Such functions can be called in the usual way as if they were methods of the original class.

https://hackernoon.com/using-kotlin-extension-functions-the-good-the-bad-and-the-ugly

https://github.com/agustarc/Android-Kotlin-Extensions/blob/master/android-view/src/main/java/github/agustarc/android/extensions/view/ViewExt.kt

https://github.com/senamit2708/Android-Kotlin-Extensions

NewUserEntryFragment.kt

    private fun saveUserDetailToDB() {
        val name = binding.txtName.text.toString()
        var mobNo = binding.txtMobNo.text.toString()
        mobNo = mobNo.addMobileExtension() //extension function
        var user = User(name = name, mobileNumber = mobNo)
        user = user.firstLetterCapital()  //extension function

        userViewModel.saveUserDetail(user)
    }

userExtension.kt

package com.example.coroutinelearning

import android.view.View
import com.example.coroutinelearning.entity.User

public fun User.firstLetterCapital(): User {
    val name = this.name.uppercase()
    return User(name = name, mobileNumber = this.mobileNumber)
}

public fun String.addMobileExtension(): String {
    return "+91- $this"
}