Kotlin: Support `assertThat(foo) { isNotNull() isNotEqualTo(bar) ... }`

It’s already possible to write nearly that by using apply:

assertThat(foo).apply {
  isNotNull()
  isNotEqualTo(bar)
}

Might it be worth a shortcut? Anecdotes welcome.

[netdpb]

Thinking a little more about foo.assertThat. I think, if we were to do it, it should not take a subject-receiver lambda, but instead a subject-parameter lambda so that it reads better as an English phrase:

// awkward. "foo: assert that is empty"?
foo.assertThat {
  isEmpty()
  contains(1, 2)
}

// better. "foo: assert that it is empty"
foo.assertThat {
  it.isEmpty()
  it.contains(1, 2)
}

// also good (imho best): "assert that foo is empty"
assertThat(foo) {
  isEmpty()
  contains(1, 2)
}

[netdpb]

Thinking further, I now think the right idiom is:

long.expression().let {
  assertThat(it).isNotNull()
  assertThat(it).isNotEqualTo(bar)
  assertThat(it).isSomeOtherThing()
}

That is very close to what I suggested above about using “it”, and uses only standard Kotlin, requiring no Truth API changes at all.

There is a small risk of someone dangling an assertion modifier off the end of the let (e.g., foo.let { ... }.inOrder()), but that could be mitigated with a check that flags any method call on a Subject whose receiver is a scope function call.