[PATCH] Move optional into the experimental namespace (first bit of the TSes)

[Marshall Clow]

On Nov 12, 2013, at 3:33 PM, Richard Smith <richard at metafoo.co.uk> wrote:

> I assume the intent is to implement this paper:
> 
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3793.html
> 
> So, assuming that include/experimental/optional was copied from include/optional (the diff doesn't say where the 'old' lines come from here)…

Yes.

> You included the inline namespace in the library synopsis comment; it shouldn't be there.

Ok.

> bad_optional_access should be in namespace std::experimental, not in namespace std.

I went back and forth about that. I agree - it _should_ be there.

However:
	The destructor for bad_optional_access lives in libc++.dylib. (due to a peculiarity in the Itanium ABI).
	If I put bad_optional_access in namespace std, then users do not need a new dylib when optional moves from std::experimental to std.

> For headers in include/support, the source files are in src/support. Should optional.cpp be moved to src/experimental/optional.cpp?

Good question. 
Header folder structure is an interface.
Source folder structure is not.

I don't see that this is necessary; but if other people really want it, I have no objection to changing it.

> Bikeshedding on the name __TSLibraryFundamentals:
>  * Should this contain a version number? We may want an ABI break at some point, and it might be nicer to have always had the version number in the name.

Yes! Crap - there was supposed to be a _v1 on the end of that.

>  * Other library-internal names in libc++ seem to use __lower_case_names
> Maybe __library_fundamentals_1?

That's fine - I can live with either one.

> Somewhat related to versioning, do we want to provide some way for people to opt into/out of individual TSes? For instance, I might want to test that my code compiles as standard C++14 (with no TSes), or to use the fundamentals TS but not the filesystem TS, since the latter has security issues.

The easy answer is not to include <filesystem>
The other answer is that's why I created the __TSLibraryFundamentals namespace.
People can hoist just one TS worth of names with "using namespace std::experimental:: __TSLibraryFundamentals;" (or whatever)

> How will we handle TSes that affect existing headers, rather than adding new ones? (Do we have any of those yet?)

Jeffrey should weigh in here, but I think that current plan is to not change existing headers.

> How will we handle TSes that need both frontend and library changes, such as the array extensions TS? It might be nice to have a single flag to the compiler ("-fsomething" or "-std=c++14+fundamentals+arrays" or something) to enable TSes for language and library as appropriate. Any ideas?

No more than you've just said.
For library-only TSes (Library Fundamentals, Networking, Filesystem), I don't think there needs to be anything done for the compiler.
For Arrays, I think a "-f ArrayTS" or something like that would work, (that flag should only work if -std=c++1y or later).

Thanks!

-- Marshall

> 
> On Tue, Nov 12, 2013 at 1:48 PM, Marshall Clow <mclow.lists at gmail.com> wrote:
> Along with C++14, the standard committee is working on several "Technical Specifications", designed to bring features that for one reason or another weren't able to be in C++14 to people before the next version of the standard (C++17??).  Those of you who remember TR1 (from about 2005) - this is a similar process under a new name.
> 
> There are several being worked on:
>         * Library Fundamentals
>         * Arrays of Runtime Bound
>         * Networking
>         * Concepts
>         * Filesystem
> 
> This patch takes the implementation of <optional> that Howard wrote and committed into libc++ (before the committee removed the feature from C++14), and moves it into the new "experimental" area, which is where these TSes will live until they are enshrined in a future version of the standard.
> 
> That area can be described as:
>         namespace std::experimental (feel free to alias this to something shorter in your code)
>         files live in the "experimental/" directory.
> 
> If you're already using the <optional> in libc++, you'll have to change your code to:
>         #include <experimental/optional>
> and
>         std::experimental::optional<T>
> 
> It's a big patch, but it's just renaming things; if I actually changed some code, then I did it wrong.
> 
> -- Marshall
> 
> Marshall Clow     Idio Software   <mailto:mclow.lists at gmail.com>
> 
> A.D. 1517: Martin Luther nails his 95 Theses to the church door and is promptly moderated down to (-1, Flamebait).
>         -- Yu Suzuki
> 
> 
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-- Marshall

Marshall Clow     Idio Software   <mailto:mclow.lists at gmail.com>

A.D. 1517: Martin Luther nails his 95 Theses to the church door and is promptly moderated down to (-1, Flamebait).
        -- Yu Suzuki

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