Re: [boost] [optional] from_optional

From: Fernando Cacciola (fernando_cacciola_at_[hidden])
Date: 2006-03-16 17:21:49

Vaclav Vesely wrote:
> Hi,
>
> There is common need of getting value from optional with possibility
> to define default value in case of the optional is uninitialized. I
> suggest two alternatives:
>
>    optional<int> o;
>    int i = o.get(123); // meber function get with additional parameter
>    int j = from_optional(o, 123); // free function
>
> Both alternatives can be implemented simultaneously.
>
> What do you think about it?
>
Hi Vaclav,

Indeed, this has been requested in the past and the fact that you can't use
an rvalue twice via the ternary operator makes it worth it.
It won't make it into 1.34 though, so I'll add it after the release.
As for the name, I like "from_optional" better than anything else, it goes
along with another pending addition:

make_optional(cond,value)

which is useful in cases when you do compute some value, but, due to some
condition (like a validity check on the value) you rather not return it; the
alternative:

cond ? optional<T>(value) : optional<T>() ;

is much much cumbersome if T is a complex type expression (and the purpose
of make_optional() is to deduce T for you).

Best

--
Fernando Cacciola
SciSoft
http://fcacciola.50webs.com/