When is it best to use `!!` over `checkNotNull`?

# stdlib

[Daniel Rust]

When is it best to use !! over checkNotNull?

[danny]

!! will throw an NPE without any context. Use require and check when validating preconditions, throwing IllegalArgument/StateException with a message of your choosing because you have external callers or want to carry more context with the message

[danny]

Use require* for incoming function arguments

[danny]

Of course if a function argument value should never be null, don't allow it to be nullable and you get the nullability check at runtime automatically

[ghedeon]

so, not a real difference unless you provide a custom message?

[danny]

NullPointerException vs IllegalArgument/IllegalStateException, but no, still fails fast - I wonder if the compiler has optimizations for argument nullability checks though

[Quy D X Nguyen]

Kotlin compiler is not that smart optimization wise