[OT] Clang seems to implement modules

[Paulo Pinto]

On Wednesday, 21 November 2012 at 00:41:39 UTC, Walter Bright 
wrote:
> On 11/20/2012 3:51 PM, Leandro Lucarella wrote:
>> Did you ever cared about reading those slides?!?!? You keep 
>> talking about
>> problems with pre-compiled headers and what Doug Gregor is 
>> suggesting are NOT
>> pre-compiled headers. Those are already in clang AFAIK.
>>
>> What he is proposing is a real module system, macros will not 
>> be re-evaluated
>> inside modules. The symbols being global have nothing to do 
>> with this being
>> pre-compiled headers.
>
>
> Modules *are* a form of precompiled headers.
>
>
>> Will this solve all the problems from C++ and make its compile 
>> time blazingly
>> fast? Probably not, but will sure help, not only to avoid 
>> reading the same
>> header over and over, but also by saving memory. But one thing 
>> is certain,
>> THIS IS NOT PRE-COMPILED HEADERS (he even mention pre-compiler 
>> headers in the
>> slides).
>>
>> For f*ck sake... Please, stop this misinformation madness.
>
> Precompiled headers are:
>
> 1. compile a bunch of .h files into a symbol table
> 2. cache the symbol table (in memory or on disk)
> 3. read the symbol table instead of reparsing the .h files
>
> Modules are:
>
> 1. compile a bunch of .h files into a symbol table
> 2. cache the symbol table (in memory or on disk)
> 3. read the symbol table instead of reparsing the .h files
>
> Yes, I understand that there are semantic differences, and many 
> differences in detail. C++11 does not support precompiled 
> headers; all ph implementations are a kludge and are not 
> standard compliant. The module proposal "legitimizes" them, 
> i.e. changes the standard so that ph can be compliant. Yes, 
> additional goodies are added like a separate scope for macros, 
> an explicit syntax for them, etc.
>
> The speed improvement should be comparable to what can be 
> achieved with a good ph system.


Ada and Modula-3 compile relatively fast, even when making use
of generics.

That is why I think using proper modules would be faster than
what is possible with pre-compiled headers.

But as refereed on my previous post, I am not a compiler expert, 
so my assumption might be wrong.

>
> Is this module proposal an improvement? I'd say yes. Is it 
> going to solve C++'s compile speed problems? I doubt it. Is it 
> a "true" module system? I don't know about that, but it doesn't 
> address things like name collisions that are imported from 
> different modules, at least not from what I saw in the slides.

That would be solvable by namespaces, I imagine.