Re: [boost] [variant] Basic rvalue and C++11 features support

Subject: Re: [boost] [variant] Basic rvalue and C++11 features support
From: Antony Polukhin (antoshkka_at_[hidden])
Date: 2013-01-13 03:58:39

2013/1/6 Joel de Guzman <djowel_at_[hidden]>:
> Hi,
>
> I just looked at the current state of variant and noticed that the
> implementation
> of recursive_variant's move ctor seems to be not as optimal as I hoped. The
> current implementation as written is:
...

I`ve finally got back from vacation, so let me add my 2 kopecks.

We can make move constructor fast and noexcept (just like Joel
proposed) and also guarantee non-empty behavior.
The idea is to delay construction of object:

T& get() {
    if (!get_pointer()) p_ = new T;
    return *get_pointer();
}

const T& get() const {
    if (!get_pointer()) p_ = new T; // mark p_ as mutable
    return *get_pointer();
}

So if move occurred object is empty, and if it is required again - it
is default constructed.

Any objections?

--
Best regards,
Antony Polukhin