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I mean, should I only use !! if dealing with legacy code?

Typically it is best to avoid using *!!* whenever possible. The main exception is testing where it is much better to discover issues early on rather than in production.

Sometimes auto-casting is not picked up, I did a not null check, further on I use the var/val my editors says it could be null. In those cases I use `!!`

<@UB5UUBMU2> Think that should only occur with `var` where the variable may have been modified between the check for not null &amp; it’s usage

<@U12FY8XH7> I also use it for nullable `val` on a class.
```
example(someClass: SomeClass) {
  if (someClass.nullableField == null) {
    throw SomeSpecificException()
  }
}

lookUp(someClass.nullableField!!)
```
The example might be weird, but I need this for an application to throw specific exceptions when this occurs.

Assigning it to a local `val` will fix this, but this is only to demonstrate

<@UB5UUBMU2> Be aware that the reason it doesn't autocast the property there is because it could be modified by another thread. For thread safety, you should use a `val` to only read the property one time. For example:
`val nullableField = nullableField ?: throw SomeSpecificException()`

New Kotlin contracts are a dealing with this. <https://proandroiddev.com/kotlin-contracts-make-great-deals-with-the-compiler-f524e57f11c?__s=cfajh45oef5g4ge15tzo>