Re: [boost] Report from Mont Tremblant C++ Committee meeting

From: Hamish Mackenzie (hamish_at_[hidden])
Date: 2005-10-19 14:04:23

On Wed, 2005-10-19 at 09:16 -0400, David Abrahams wrote:
> > Do you think the "fill" example would be useful to fill missing
> > values in vector< OptionalPointee >?
> 
> Sorry, I don't understand.

Sorry I was in a hurry and didn't describe what I was thinking better.
Here is the example from the other email.

template< typename OptionalPointee, typename Value_Type >
Optional_Pointee fill( Optional_Pointee x, Value_Type & default_value )
{
  if( x == none )
  {
    x = &default_value; // Does this work with optionals?
  }

  return x;
}

You might use it like this...

std::vector< int * > x1;
std::vector< optional< int > > x2;
...
int default_value = 5;

// I imagine this currently fails due to ( x == none )
std::transform( x1.begin(), x1.end(), x1.begin(),
        fill( _1, default_value ) );

// And this probably fails due to x = &default_value
std::transform( x2.begin(), x2.end(), x2.begin(),
        fill( _1, default_value ) );

I am not using this as an argument against the use of * and ->.  I was
just wondering if we could make the above (or something similar) work.

Hamish