[jamming] Jam2.5 and precompiled headers

Chris Antos chrisant at windows.microsoft.com
Tue Feb 11 11:14:08 PST 2003


Richard, Christopher, and I discussed the "on" thing in private emails a
couple weeks ago.  They agreed on the central point, and I think 2.5 is
supposed to include the central fix.

We disagreed on secondary design points, and both our positions are
defensible, although I'm biased and think mine is "more" defensible.
;-)

Anyway, the central fix is enough to solve the root of the problem,
although you won't be able to use my Jambase as-is.  It will need an
extra line before anyplace that I used the "VAR on $(x) += $(y)" syntax:

VAR on $(x) ?= $(VAR) ;

That will copy the global value of $(VAR) into the "VAR on $(x)" first,
if "VAR on $(x)" has not yet been populated.  Otherwise the initial "+="
will merely set the new target-specific value and obscure the global
value, thus not doing what the rule writer intuitively expects.  Without
the central fix, the "?=" line above won't work properly.

My private version's "+=" automatically copies the global value first if
appropriate, at least until someone can show me an example where it
would not be the Right Thing to do.

Cheers,
// chris


-----Original Message-----
From: Jacob Gorm Hansen [mailto:jg at ioi.dk] 
Sent: Tuesday, February 11, 2003 4:57 AM
To: Chris Antos
Cc: Matt Armstrong; jam mailling list
Subject: RE: [jamming] Jam2.5 and precompiled headers

On Thu, 2003-01-23 at 23:37, Chris Antos wrote:

> So absolutely Jam should contain rules for using precompiled headers
> using MSVC.  Don't knock it until you've tried it (for a baseline, you
> should test the pch perf wins outside of Jam as a baseline for what
Jam
> should be able to _beat_; because Jam adds perf wins of its own).

Naturally, I agree. You mentioned in a private post that there is a bug
in Jam with regards to the 'on' keyword not correctly restricting its
scope. Can you elaborate on this bug and how to fix it?

thanks,
Jacob




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