good morning ! What the "!!" means ?

# android

[Fernando de Paula]

good morning ! What the "!!" means ?

[Umar Ata]

https://kotlinlang.org/docs/null-safety.html

[Fernando de Paula]

thanks!!!

[Syed Ovais Akhtar]

? Means can be null and !! Means can't be null
For example we have locations which can be null so we can write

location?.let {
// do something if not null

} ?: run {
// Do something if null
}

And
location!! // Is not null
@Fernando de Paula

[Umar Ata]

location!! will produce crash if it is null
it is only use when you are sure that property will not be null at a particular condition

[Kamil Kalisz]

!! cast nullable object to non nullable object. If that object is null that operation will throw NullPointerException

[Syed Ovais Akhtar]

@Umar Ata of course yes

[Fernando de Paula]

very nice!

[Fernando de Paula]

it is dangerous

[Umar Ata]

try to avoid using !! and just use location?.let{
print(it.lat)
}
and this let will only trigger when location is not null

[Fernando de Paula]

"it" is like "this" ?

[Syed Ovais Akhtar]

It keyword will makes reference of location variable

[Kamil Kalisz]

it depends of method. let/run/apply etc…

[Kamil Kalisz]

https://kotlinlang.org/docs/scope-functions.html#function-selection

[Umar Ata]

https://www.google.com/url?sa=i&url=https%3A%2F%2Fstackoverflow.com%2Fquestions%2F45[…]e=images&cd=vfe&ved=0CAsQjRxqFwoTCKi8-ozH1vMCFQAAAAAdAAAAABAD

[nfon jeannoel]

Way of assuring that the value will not be null. This is to bypass the null check

[gildor]

I recommend #getting-started for such discussions, Android channel doesn’t look relevant to this