Re: [boost] [type-traits] aligned_storage in unions

Subject: Re: [boost] [type-traits] aligned_storage in unions
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2010-09-17 15:12:10

AMDG

OvermindDL1 wrote:
> On Fri, Sep 17, 2010 at 9:46 AM,  <dherring_at_[hidden]> wrote:
>   
>> On Fri, 17 Sep 2010, Frank Mori Hess wrote:
>>     
>>> What about using boost.variant instead?
>>>       
>> It doesn't satisfy my need for everything to be in-place (e.g. for seamless
>> use with shared memory, memory pools, etc.).  [Note: we don't actually use
>> std::string; it was just convenient for the example.]
>>     
>
> How is it not in-place?
>
> If C++ supported unions containing anything, then
> boost::variant<int,std::string,myClass> would be identical in layout
> to:
> struct {
>     uint which;
>     union {
>         int i;
>         std::string s;
>         myClass m;
>     }
> }
> Which all use the same memory.

boost::variant can use the heap in some cases,
to preserve exception safety.

In Christ,
Steven Watanabe