Re: [boost] [Operators] empty_base should be untemplated?

Subject: Re: [boost] [Operators] empty_base should be untemplated?
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2013-09-21 17:41:09

On 20 Sep 2013 at 23:00, Michael Marcin wrote:

> > VS2012 doesn't appear to do empty base class optimization for multiple
> > inheritance at all, so templated/untemplated also makes no difference here.

I believe the /vmm compiler flag will fix that 
(http://msdn.microsoft.com/en-us/library/bkb78zf3.aspx) at the cost 
of breaking ABI. In essence, due to backwards ABI compat constraints 
requiring the default /vmv option, MSVC can only collapse a single 
empty base class, not more than one.

In other words, it's a feature not a bug :)

I absolutely agree though that when they moved to 64 bit they should 
have fixed this. They fixed lots of long standing ABI problems with 
the 64 bit move, but I believe not this one sadly.

Niall

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