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

[cpovirk]

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.

[cpovirk]

I'm reliably informed that the implementation would be something like:

operator fun <T: Subject> T.invoke(assertions: T.() -> Unit): Unit = this.assertions()

[JakeWharton]

Yep, that'll work!

I also flip the parameter to a receiver, but that requires one extension per subject type instead of the invoke trick.

[vRallev]

@JakeWharton Is this what you mean?

fun assertThat(string: String, assertions: StringSubject.() -> Unit) {
  assertThat(string).run { assertions() }
}

This would allow

assertThat("hello") {
  isNotEmpty()
  isEqualTo("hello")
}

[JakeWharton]

No. The parameter becomes a receiver of the extension.

fun String.assertThat(assertions: StringSubject.() -> Unit) = assertThat(this).assertions()

[vRallev]

Got it. Then it reads differently, though. But that's a matter of taste I guess.