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From Martin Sebor <>
Subject Re: _RWSTD_VER value on trunk
Date Thu, 13 Dec 2007 21:24:20 GMT
Andrew Black wrote:
> Martin Sebor wrote:
>> This has been bugging me -- when someone checks out trunk, does a build and
>> sends
>> us build results, we have no way of telling that the build results are, in
>> fact, for trunk and
>> not for 4.2.0 (or the head of 4.2.x), because the value of _RWSTD_VER is the
>> same. I
>> think we should change it so that the value is unique for each branch, or at
>> least distinct
>> from any release.
>> Any suggestions for what would be a good value?
> The following is my suggestion for a scheme for _RWSTD_VER:
> Trunk: 0xFFFFFFFF
> Trunk feature branch: 0xFFFFFFxx
> Major branch: 0xMMFF0000
> Maintenance branch: 0xMMmmFF00

Thanks, this is an interesting idea that I hadn't thought of.
At first I didn't think 0xFF made sense but I'm slowly starting
to warm up to it.

> A trunk feature branch is a branch in subversion used for developing a
> specific feature, which isn't ready for inclusion in trunk, but is major
> enough that incremental testing is required.  An example could be the
> implementation of concepts.  The placeholder 'xx' is a non-FF value,
> unique to a feature branch.  If the number of feature branches exceeds
> 255, it will be necessary to reuse numbers, but this isn't a likely
> occurrence in the near term.  These numbers should be issued in the
> order the branches are created.

We'd have to find a way to avoid conflicts. I.e., How would one go
about finding the next available value of xx to grab for their new
feature branch? (It wouldn't be too hard to do today but if we had
as many feature branches as gcc, as unlikely as it is, it could be
a challenge.)

> A major branch is a branch in subversion used for ongoing development of
> a source compatible lineage.  The placeholder MM represents the major
> version.  An example would be ongoing maintenance of the 4.x version of
> stdcxx beyond 4.3, after the 5.0 release has been made.  In the case of
> a 4.x maintenance branch, the version would be 0x04FF0000

Makes sense.

> Maintenance branches are an established concept, with the 4.2.x branch
> being an example.  The placeholder MM represents the major version, with
> the placeholder mm representing the minor version.  In the case of
> 4.2.x, the version would be 0x0402FF00.

Same here.

> Justification:
> My primary reason for using the 0xFF value as a placeholder (generally)
> is because it is greater than any particular released version number.
> This should allow checks which look for a specific version of the
> library (either older or newer) to function correctly.  If someone
> wanted to exclude the trunk from these checks, it would be possible to
> simply perform a bitwise negation, and if the value of that negation is
> 0, it means the token references a trunk version.

I think I like this idea quite a bit, actually Using a fixed value
also makes it easy to test for it in release scripts and catch
releases where the macro isn't set correctly (because the value
would either be 0xFF or fail to match the version in the name of
the tag).

Is everyone else happy with this scheme?


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