Difference between with, run, let, also and apply in Kotlin.

diff_of_run_let_also_apply.kt

/**
 * Difference between with, run, let, also and apply in Kotlin.
 * 
 * Official doc: https://kotlinlang.org/docs/scope-functions.html#functions
 *
 * Awesome blog posts:
 * - https://www.journaldev.com/19467/kotlin-let-run-also-apply-with
 * - https://medium.com/@fatihcoskun/kotlin-scoping-functions-apply-vs-with-let-also-run-816e4efb75f5
 * - https://medium.com/@elye.project/mastering-kotlin-standard-functions-run-with-let-also-and-apply-9cd334b0ef84
 */

import kotlin.random.*

fun main() {
    
    var name = "Shohag"
    
    // with()
    // --------------------
    // Inside: Change instance properties without the need to call dot operator.
    // Context: The context object is available as a receiver `(this)`.
    // Return: The return value is the lambda result.
    var with_return_result = with(name) {
        // ...
        
        // name.length
        // or, just:
        length // <-- returned result of this
    }
    
    println(with_return_result)
    
    
    // run()
    // --------------------
    // Inside: change instance properties without the need to call dot operator.
    // Context: The context object is available as a receiver `(this)`.
    // Return: The return value is the lambda result.
    var run_return_result = name.run {
        // ...
        
        // name.length
        // or, just:
        length // <-- returned result of this
    }
    
    println(run_return_result)
    
 
    // let()
    // --------------------
    // Inside: Use `it` or `anyCustomName`
    // Context: The context object is available as an argument `(it)`.
    // Return: The return value is the lambda result.
    var let_return_result = name.let { anyCustomName ->
        // ...
        
        anyCustomName.length // <-- returned result of this
    }
    
    println(let_return_result)
    
 
    // also()
    // --------------------
    // Inside: Use `it` or `anyCustomName`.
    // Context: The context object is available as an argument `(it)`.
    // Return: The return value is the object itself.
    var also_return_result = name.also { anyCustomName ->
        // ...
        
        println("Name length: ${anyCustomName.length}")
    }
    
    println(also_return_result)
    
 
    // apply()
    // --------------------
    // Inside: Use `this`, `this` can be ommited.
    // Context: The context object is available as a receiver `(this)`.
    // Return: The return value is the object itself.
    var apply_return_result = name.apply {
        // ...
        
        println("Name is: ${this}")
        println("Name length: ${length}")
    }
    
    println(apply_return_result)
    
    // takeIf() and takeUnless()
    // --------------------
    // `takeIf` will take the object if the predicate is `true` and `takeUnless` will not take the object if the predicate `true`.
    // 
    // Context: The context object is available as a lambda argument `(it)`.
    val number = Random.nextInt(100)

    val evenOrNull = number.takeIf { it % 2 == 0 }
    val oddOrNull = number.takeUnless { it % 2 == 0 }
    
    println("even: $evenOrNull, odd: $oddOrNull")
}