"opaque types" introduced without documentation

[lll000111]

New Features:

• Added support for opaque type aliases

So.... what is this? "opaque" indeed :-)

Version 0.51 commit message: 7da11c3

[rkurbatov]

👍

[AugustinLF]

Not docs, but better than nothing: https://twitter.com/vkurchatkin/status/886385324422836224

[billschaller]

@jbrown215

[jbrown215]

We'll be working on the documentation this week. Until that gets landed, the hack documentation for their opaque type aliases covers the functionality we were going for. For some examples of the syntax and how opaque types work in Flow, you can check out anything in the tests/ directory that starts with opaque.

I've been focusing on getting support for this landed in babel/babylon so that you can start using it ASAP.
Heres links to those PRs, in case you wanted to follow along:
babel/babel#5990
babel/babylon#644
babel/babylon#643

[jbrown215]

Docs landed: 9bac97f

https://flow.org/en/docs/types/opaque-types/