Re: [boost] File Handle and FILE* wrappers?

On Nov 29, 2014, at 6:16 AM, Olaf van der Spek wrote:

On Wed, Nov 26, 2014 at 9:28 PM, Josh Juran wrote:

...

I use POSIX I/O calls frequently. I adapted Lisa Lippincott and Marshall Clow's work on Nitrogen to create a library called poseven, based on the same 'nucleus' core library. p7::fd_t is an enum type for a file descriptor, and n::ownedp7::fd_t and n::sharedp7::fd_t are smart resources that work like unique_ptr and shared_ptr (loosely speaking) respectively. Much of it is about a decade old, early in my exposure to generic programming, though just recently I added p7::coprocess.

Interesting. Why are you using an enum to store the fd?

For type-safety and efficiency. I don't use int, because that would allow any constant to be misinterpreted as a file descriptor. Nitrogen used to use complicated wrapper classes, but these had several defects: (a) they were slow to compile in the compiler used at the time (and which I still use for classic Mac OS development[1]), (b) the same compiler wouldn't place their values in registers, (c) their values couldn't be used in switch statements, and (d) creating constants for them was problematic, typically resulting in many `static const Foo x = Foo( ::x );` in headers. Using an enum addressed all of these issues (with (d) being at least a partial improvement). One of the downsides of C-style enums is non-portable memory layout. You can ensure an enum is large enough my declaring max_Foo = uint32_t( -1 ), but there's no guarantee that enum Boolean { False, True } occupies a single byte instead of, say, four. I'm new to C++11, but if I understand correctly, its enum classes address this very issue.

Do you think it'd be useful to move parts of this functionality into Boost?

Quite possibly. Poseven is useful if you want to add type-safety and exception-safety to a C-style POSIX codebase (or subset thereof) without rewriting it to use higher-level semantics like ASIO. In debug mode, it throws exceptions containing a backtrace. A key question is how to approach the overlap of poseven with existing Boost libraries like Filesystem and Thread. I think the first step toward adoption would be for me to familiarize myself with Boost.System. Josh [1] Classic Mac OS is relevant in that POSIX programs are supported through MacRelix. The latest compiler to fully support classic Mac OS is Metrowerks C++ 2.4.1 from CodeWarrior Pro 6.3, released in summer 2000.