Re: [Boost-users] variant has non-trivial destructor even when all constituents have trivial destructor

Subject: Re: [Boost-users] variant has non-trivial destructor even when all constituents have trivial destructor
From: 谢任中 (joshchia_at_[hidden])
Date: 2015-11-27 23:27:06

I used integers only to keep the example simple.

In reality I have a few structs with trivial copy-assignment operator and
trivial destructor that I make members of the variant. variant lets me use
static visitors.

If I use my own union with switch statements instead of variant with static
visitors, when I add a new type to the union, I may forget to update some
switch statement but with static visitors I'll get a compiler error if I
forget to update any static visitor.

The code may be simpler in some sense if I use a union but it's safer and
more maintainable if I use a variant, especially if I would have to
maintain many switch statements.

I could implement my own static visitor mechanism just for this union-ish
type but that seems like reinventing the wheel.

So, it would be convenient if I could use
boost::lock_free::queue<variant<...>> on my structs, although I have barely
any idea on the implementation complexity required.

On Fri, Nov 27, 2015 at 11:11 PM, Agustín K-ballo Bergé <
kaballo86_at_[hidden]> wrote:

> On 11/26/2015 11:58 PM, ☂Josh Chia (谢任中) wrote:
>
>> It seems that boost::variant has non-trivial destructor even for
>> something like boost::variant<int32_t, int64_t>. Thus, It cannot be used
>> in situations that call for a POD where calling the destructor is trivial.
>>
>> Particularly, I can't have a boost::lock_free::queue<boost::variant<X,
>> Y>> even both X and Y are trivially destructible.
>>
>
> Just making `variant` trivially destructible would not be enough, as
> `boost::lockfree::queue` also requires a trivial copy-assignment operator.
>
> How about making boost::variant trivially-destructible when everything
>> in it is trivially-destructible?
>>
>
> For your particular use case, it would be far simpler to just use plain
> old discriminated-unions.
>
> Regards,
> --
> Agustín K-ballo Bergé.-
> http://talesofcpp.fusionfenix.com
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