Review OS\ - is it actually 'POSIX-like'?

[fredemmott]

Full design goals/notes at https://github.com/hhvm/hsl-experimental/blob/daf9f470109b6728a9ac998c8f964a32663a08e2/src/os/README.md#api-design-notes

TL;DR: aiming for a relatively small number of rules determining how OS\ differs to posix, assuming the function is a posix function. These include:

• throw exceptions on errno
• if a function returns 0 on success, 1 on failure, return void, given it will never return 1 (it'll throw)
• replace out parameters with tuple returns
• wrap types if needed for seciurity, e.g. OS\FileDescriptor instead of ints

In particular, I'm aiming for no need to learn function-specific stuff.

• 'Host byte order' in the network stuff is borderline for this IMO.
• is there other stuff?

If there's other stuff, we should either:

• change it to be more POSIX-like
• stop trying to be POSIX-like, and make friendlier OS\ APIs

[fredemmott]

Need to review all functions/files for this systematically. Will grep/sed a checklist when I get to this.

[fredemmott]

In terms of signatures, I believe this is still consistent.

From a usability perspective, it might be good to codegen constants from enums- e.g. OS\EINVAL == OS\Errno::EINVAL