are there plans to leverage contracts? i find i d...

# kotlintest

[bbaldino]

are there plans to leverage contracts? i find i do something like this here and there:

val result = func(): String?
result shouldNotBe null
result as String
result.startsWith("...") shouldBe true

[bbaldino]

it'd be nice to have a contract for shouldNotBe null so wouldn't have to explicitly cast

[bbaldino]

well, maybe this is a dumb use case, i could just use ?. there, but, given i've asserted it's already not null it'd be a nice-to-have

[sam]

I thought we'd added that already

[sam]

@LeoColman ?

[LeoColman]

We added for shouldBeInstanceOf

[LeoColman]

I think contracts are not smart enough for shouldNotBe null yet

[LeoColman]

Cause we'd have to say "if paramaeter is null and this returns, it wont be null"

[LeoColman]

And this is impossible afaik

[LeoColman]

@bbaldino use shouldBeInstanceOf

[sam]

Isn't should not be null the same as if (a ! =null) { } ?

[LeoColman]

Yes, but you can also use foo shouldNotBe bar

[bbaldino]

i was just playing with this:

@ExperimentalContracts
fun foo(x: Any?) {
    contract {
        returns() implies (x != null)
    }
    if (x == null) {
        throw Exception()
    }
}

[LeoColman]

And i cant create a contract for both cases

[bbaldino]

which works with

val x: String? = null

        foo(x)
        x.startsWith("asdsd")

[bbaldino]

but maybe that's not a good approximation of the flow in shouldNotBe

[bbaldino]

i just kinda took a quick look at it

[LeoColman]

Let me get to my pc and I'll explain some cases that wouldnt work

[LeoColman]

Hm... Perhaps it's not actually a problem for the shouldNotBe case?

[LeoColman]

I was fearing that people would not be able to use a shouldNotBe b if b was null

[LeoColman]

But a shouldNotBe b will always fail if b is null and a is null, so that's ok

[LeoColman]

And if a is not null, then it will never fail

[LeoColman]

Yeah, perhaps that works

[LeoColman]

Thinking again...

[LeoColman]

With the code

[LeoColman]

val a: String? = "foo" // A is not guaranteed to not be null

a shouldNotBe "Bar"

a.length shouldBe 125

[LeoColman]

This will fail, because the contract will say that "If shouldNotBe returns, a is not null"

[LeoColman]

What we can do is a.shouldNotBeNull()

[LeoColman]

And we already have that feature

[LeoColman]

fun Any?.shouldNotBeNull() {
  contract {
    returns() implies (this@shouldNotBeNull != null)
  }

  this shouldNot beNull()
}

[LeoColman]

And it already has the contract, so idk

[LeoColman]

I closed the issue. I don't think this is possible with the current contracts.

[bbaldino]

oh, i don't see shouldNotBeNull, is it in a recent update?

[bbaldino]

but that's good to know, thanks

[LeoColman]

Perhaps it wasn't published yet? I'm not sure

[LeoColman]

Which version are you using? I'm pretty sure it's in the latest version

[bbaldino]

3.3.0

[bbaldino]

oh, nm

[bbaldino]

my other project (where i check before) is on an older one

[bbaldino]

i do see it in 3.3.0