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Subject: Re: [boost] [testing] Add a tester with hidden visibility
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2015-05-07 14:48:32

On 7 May 2015 at 19:10, John Maddock wrote:

> > I suspect that C++ Modules cannot deliver any improvements over the
> > non-header only with precompiled headers configuration. Good build
> > config always beats compiler magic.
> Actually it can - if implemented well - way back when, Borland's C++
> compiler had better PCH support than anything else out there, it wasn't
> quite C++ modules, but it was quite a decent part of the way there.
> They had a little server app that managed and loaded all required PCH's
> as AST's into memory, so when a file was being compiled it would just
> map the memory from the other process and start compiling from there.
> It was lightning fast with near enough instant compile times. And this
> was 10+ years ago on hardware that folks would laugh at today. It was
> more or less automatic too - if there were no changes to a files
> #includes it would just go ahead and cache everything till after the
> last #include without the user having to excplicitly mess with PCH's at
> all. Of course both templates and C++ in general are a lot more complex
> now: this was all pre-STL days! Still it would be nice, if we could
> have a compiler/IDE release that wasn't actually 3 times slower than the
> one before ;)

It looks like I accidentally deleted a subsequent paragraph about C++
Modules being more likely useful as a step towards next gen tooling

My C++ Now 2014 white paper ( detailed
how one might implement a C++ compiler as a database of ASTs such
that all C++ was always as if inline defined i.e. every bit of code
could see all other C++ code anywhere on the system. Build and
dependency management simply become graph database queries.

I think one of the C++ Now 2015 talks might cover some actual work
done on such a database repository of ASTs to implement a build and
package manager (this one?, it's ultimately
where Link Time Optimisation must eventually end up anyway when
pushed to extremis. Might as well get a JIT zero time build system
for free out of it. I guess the question eventually becomes if the
compiler vendors are game for implementing such a very complex tool.


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