Re: [boost] [optional] Types without assignment operator

Subject: Re: [boost] [optional] Types without assignment operator
From: Andrzej Krzemienski (akrzemi1_at_[hidden])
Date: 2012-11-14 06:52:27

2012/11/14 Adam Badura <abadura_at_[hidden]>

>
> So instead of accessing the object directly I always access it by a
> function. That function first checks if the object is already constructed
> (boost::optional is initialized) and if so just returns it. Otherwise it
> first constructs it.
>

I am having problems imagining the situation. Can't you change your
function so that returns real object rather than optional object if it is
initialized? Perhaps using optional reference to an object would solve your
problem?

> Now the Synopsis part of the Boost.Optional documentation does mention
> (Typed)InPlaceFactory assign operators which do look promising for solving
> this issue. But firstly they are not documented in following Detailed
> Semantics part. There is even no link in the Synopsis. (Is this docs bug?
> In which part? Missing docs or extra functions?)

See this link:
http://www.boost.org/doc/libs/1_52_0/libs/utility/in_place_factories.html
Indeed, there is no path to it from the documentation root.

> And secondly (Typed)InPlaceFactory support is "intrusive". I cannot add it
> to a class without changing the class itself. And in my case I cannot
> change the class (boost::program_options::options_description - why cannot
> it be copy assigned, that I don't know...). Maybe adding some extra wrapper
> would help but I don't think it would be a solution. Rather a somewhat ugly
> workaround.
>

Intrusive? "in_place" is used to initialize or assign boost::optional. Do
you want to use it for your own class? THis does not appear the right way
to go.

Regards,
&rzej