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Subject: Re: [cppcon]
From: Tjernstrom, Staffan (Staffan.Tjernstrom_at_[hidden])
Date: 2019-09-12 13:51:03


Whilst this would obviate the need for the layout marker, it would be a maintenance nightmare. Consider what would happen when you add 2 screenfuls of methods in between the members, along with say 10-20 members. Trying to thread the needle to correctly insert a new member would basically be impossible.

From: SG14 [mailto:sg14-bounces_at_[hidden]] On Behalf Of Edward Catmur via SG14
Have you considered the low-level approach of allowing the user to specify the exact location of fields within a class, perhaps by an extension to the bitfield syntax?

In your example,

struct A {
    // Feature A documentation
    bool feature_a_enabled : 30, 1;
    unsigned int feature_a_value : 16, 14;

    // Feature B documentation
    bool feature_b_enabled : 31, 1;
    unsigned int feature_b_value : 0, 16;
};

So the bitfield syntax would become : [offset, ] width where the offset is in bits from the beginning of the class.

Of course, overlap would need to make the program ill-formed.

On Mon, Sep 9, 2019 at 8:00 PM Rene Rivera via SG14 <sg14_at_[hidden]> wrote:
My entry for the agenda at the CppCon meeting is...

"Member Layout Control"
<https://raw.githack.com/grafikrobot/papers/master/wg21/member_layout/member_layout_D1605R0.html>

It's "rough" first attempt at this. But it's good enough for discussion.


--
-- Rene Rivera
-- Grafik - Don't Assume Anything
-- Robot Dreams - http://robot-dreams.net
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