Re: Optional library

From: anshu khare (anshukhare1998_at_[hidden])
Date: 2020-01-19 11:59:30

When I run the following code :

int i = {};
boost::optional<int> v = i;
cout << get_optional_value_or(v, 1)

I get a compilation error in the third line.

On Sun, 19 Jan, 2020, 5:12 PM Mateusz Loskot via Boost, <
boost_at_[hidden]> wrote:

> On Sun, 19 Jan 2020 at 11:57, anshu khare via Boost
> <boost_at_[hidden]> wrote:
> > But when I run
> >
> > const std::string i = {};
> > boost::optional<const std::string&> str = i;
> > cout << get_optional_value_or(str, "some other string") ;
> >
> > The output is an empty string.
> > Shouldn't it give "some other string as output"
>
> No, it should not.
>
> From the documentation:
> "Class template optional is a wrapper for representing 'optional' (or
> 'nullable')
> objects who may not (yet) contain a valid value."
>
> An empty string in `i` variable IS a valid value, so `str` is set with
> a valid value,
> Since it is valid value, get_optional_value_or returns that valid value
> and not the "some other string".
>
> > because if I run the same
> > code with integer it gives the second parameter of
> get_optional_value_or()
> > as output?
>
> Are you sure?
>
> This is expected to print 0, the valid value of `i` and not the default 1:
>
> int i = {};
> boost::optional<int> v = i;
> cout << get_optional_value_or(v, 1);
>
> Best regards,
> --
> Mateusz Loskot, http://mateusz.loskot.net
>
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