Add doBlocking() utility method for running coroutines.

[kevinhwang]

This is a useful utility method used in places where you want to run a coroutine for its side effect.

E.g.,

fun main() = doBlocking {
  // ...
}

@Test
fun myTest() = doBlocking {
  // ...
}

With runBlocking(), if the last line of the coroutine block being run doesn't evaluate to Unit, e.g.:

fun main() {
  runBlocking {
    // ...
    Unit
  }
}

the compiler will complain about being unable to infer the type variable T of the block. Inserting a "return value" of Unit at the end is necessary to tell the compiler the block's return type.

Similarly, if you do

@Test
fun myTest() = runBlocking {
  // ...
   Unit
}

without the explicit Unit "return value" at the end, if the last line evaluates to a non-unit type, you'll get a type mismatch error, or the compiler will infer myTest()'s return type to be non-Unit.

[dkhalanskyjb]

The expected way to use runBlocking in main is

fun main() {
    runBlocking {
        // your code
    }
}

the compiler will complain about being unable to infer the type variable T of the block.

Could you provide a specific example?