Why the code in an object expression can access variables from the scope that contains it in kotlin?

Question

In Kotlin,the code in an object expression can access variables from the scope that contains it, just like the following code:

fun countClicks(window: JCompo         


        

Answer 1

IF you dump the class by using javap you can found kotlin using a IntRef not a int for lambda accessing the mutable variable out of its scope, since in java variables out of the lambda scope are effectively-final or final which means you can't modify the variable at all, for example:

// Kotlin 
var value = 1; // kotlin compiler will using IntRef for mutable variable
val inc = { value++ }; 
inc();
println(value);// 2;

//Java
IntRef value = new IntRef();
value.element = 1;

Runnable inc=()-> value.element++;
inc.run();
println(value.element);// 2;

the code above are equality. so don't modify the mutable variables out of the lambda scope in multi-threads. it will resulting to the wrong result.

another good usage is you needn't modify the mutable variable out of the lambda scope and want to improve the performance optimization. you can use an additional immutable variable to achieve the performance for the lambda , for example:

var mutable = 1;
val immutable = mutable; // kotlin compiler will using int 

val inc = { immutable + 1 };