Hello, World! Hey I was looking at contracts agai...

# announcements

[bod]

Hello, World! Hey I was looking at contracts again (even though they're still experimental), and couldn't find a way to do what I want, so I'm wondering if it's possible. I have a fun parseDate(dateStr: String?): Date? and want to express that if dateStr is null then the result will be null - and also the opposite. Possible?

[rafi]

When you say "the opposite", does it mean that "if dateStr is not null then the result will not be null" ? If yes it seems risky since dateStr could be malformed

[bod]

Yes that's what I mean. Let's ignore the malformed case for now (I think this will be handled by throwing, not by returning null)

[rafi]

Something like returnsNotNull() implies dateStr != Null maybe ?

[bod]

I've tried, but it's still red if I do something like val d: Date = parseDate(nonNullStr)

[bod]

(red because parseDate can return null according to the compiler, even though it's not possible in that case)

[dmitriy.novozhilov]

Contracts works in opposite way. Contract returnsNotNull() implies dateStr != Null means that "if call parseDate(str) returned not null than `str != null`"
There is no support of contracts that you want but we are considering support this case

[bod]

Thanks a lot for chiming in. It may be just me but I have the impression that this use-case would be one of the most common ones.