I believe that Ruby also has that & shortcut (or similar) but it's totally unreadable. I never used it and I don't even want to check the exact syntax. Is it the only way it works in Crystal?

It being readable is a matter of getting used to it. I find it more readable than the block version as there is less syntactic boilerplate. YMMV.

Ruby has a similar version using colon instead of dot but that version isn't chainable and doesn't take arguments so it can't do the *2.

And no, you can write out the full block just as you did in the Ruby version.

Whoops, you're right.

    "1 2 3".split(' ').map { it.toInt() * 2 }