Re: [boost] [optional] little addition

Subject: Re: [boost] [optional] little addition
From: Niels Dekker - mail address until 2010-10-10 (niels_address_until_2010-10-10_at_[hidden])
Date: 2009-02-27 07:04:45

Arno Schödl wrote:
> I just started using boost::optional, and this proved to be
> generically useful, but I believe is currently not in
> boost::optional:
>
> template< class T, class Tcompatible >
> bool optional_assign(
>   T& t, boost::optional<Tcompatible> const& optt) {
>     if( optt ) {
>       t=*optt;
>       return true;
>     } else {
>     return false;
>   }
> }
>
> so you can write
>
> boost::optional< TMyValue > TryToGetT();
> T t;
>
> if( !optional_assign( t, TryToGetT () ) {
>    ... other way to get t ...
> }

Are you sure you want to do a copy-assignment of your T?  Your example 
would typically be more efficient when doing a move-assignment or a swap 
instead.  What would you think of an optional<T>::swap_if_initialized 
member function, so that you can do:

  if( ! TryToGetT().swap_if_initialized(t) {
    ... other way to get t ...
  }

Implemented as:

  bool swap_if_initialized(T& arg)
  {
    if ( *this )
    {
      // Using the Boost Swap utility:
      boost::swap(**this, arg);
      return true;
    }
    return false;
  }

Kind regards, Niels

--
Niels Dekker
http://www.xs4all.nl/~nd/dekkerware
Scientific programmer at LKEB, Leiden University Medical Center