Subject: Re: [boost] [Range] Range adaptor approach for temporary range lifetime issue
From: Dave Abrahams (dave_at_[hidden])
Date: 2012-06-22 14:37:12
on Sun Jun 17 2012, Michel Morin <mimomorin-AT-gmail.com> wrote:
> Dave Abrahams wrote:
>>> Side note:
>>> * There is also a fully automatic approach (i.e. when an rvalue range
>>> is adapted,
>>> `moved_range` is automatically used without piping it to `moved` adaptor).
>>> But this approach incurs unnecessary overhead when passing them to functions,
>>> because function arguments do not have the lifetime issue and we don't need
>>> to use `moved_range`. So I prefer the "manual" approach.
>> Could you illustrate this with an example? Â I'd like to understand the
>> trade-off you're making.
> Here is an example of the manual approach:
> template <typename Range> void f(Range&&);
> // No lifetime problem.
> f(std::string("Hello world!") | reversed);
> // `moved` is not necessary.
> f(std::string("Hello world!") | moved | reversed);
> In the automatic approach, `std::string("Hello world!") | reversed` returns
> `moved_range<std::string, boost::fusion::vector<reverse_forwarder> >`.
As opposed to what? You haven't shown me what it returns in the manual approach.
> So there is unavoidable overhead (i.e. moving a temporary container
> into range adaptors) in `f(std::string("Hello world!") | reversed);`.
Also, I don't know enough about these types to see the overhead. More
detail would be appreciated.
-- Dave Abrahams BoostPro Computing http://www.boostpro.com
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