Question. Kotlin requests to check nullable membe...

# getting-started

[tateisu]

Question. Kotlin requests to check nullable member property every time refer to it even it is initialized in same function. Is there a way to avoid this?

// I have to copy to local variable
fun menberFunction(){
    var x = this.x
    if( x == null ){
        x = X()
        this.x=x
    }
    codeUsingX(x)
    // this.x may reset to null outside of this function.
}

// I want just using  this.x
fun menberFunction(){
    if( x == null ) x = X()
    codeUsingX(x)
    // this.x may reset to null outside of this function.
}

[Andreas Sinz]

do it this way: val x = this.x ?: X()

[Andreas Sinz]

then you have an immutable non-nullable X

[tateisu]

it's same thing about using local copy. also I still have to write

this.x=x

[Andreas Sinz]

what are you trying to accomplish?

[tateisu]

don't create local copy, just use this.x.

[Andreas Sinz]

but you need to assign a new value when its null and afterwards use it like a non-nullable var?

[tateisu]

If it is obvious that this.x is not manipulated externally while executing the function, It would be nice to have a way to express it. That way we do not need extra copies or null checks or wrapper function.

[Andreas Sinz]

the compiler is not able to infer that this.x isn't manipulated during the execution of the functions

[Andreas Sinz]

why is this.x nullable?

[tateisu]

this.x may reset to null outside of this function. it may use many system resource.

[tateisu]

If the compiler can not handle this problem correctly at this time, we should compromise with local copy

[Andreas Sinz]

yes, the easiest way is to use a local property. I'm curious: What system resources are you using, that you need to be able to go back and forth between null and X()

[tateisu]

Actually, X will be given different arguments each time it is created. The lifecycle of caller and X is very different. I think that it is reasonable to use Nullable in this case

[Andreas Sinz]

that sounds like you are violating the Single Responsibility Principle

[tateisu]

I am not interested in your religion.

[Andreas Sinz]

lol

[Andreas Sinz]

its not about "religion", its about good software design