Re: [Boost-users] [Boost.Assign] list_of::range without an initial (single) element?

Subject: Re: [Boost-users] [Boost.Assign] list_of::range without an initial (single) element?
From: Michael McNeil Forbes (michael.forbes_at_[hidden])
Date: 2010-06-17 17:54:53

Thorsten Ottosen wrote:

>> In that case, I'm confused about why list_of<int>() inserts a  
>> default value.
>
> It was a consistency issue. Consider
>
>  list_of<int>()(42); // 0, 42
>  list_of<int>(42)(); // 42, 0
>  list_of(42)();      // 42, 0
>
> would you expect that to be any different?

I suppose the only consistent interpretation would be for either () to  
be a no-op (no default's)

Proposal 1:
  list_of<int>()(42); // 42
  list_of<int>(42)(); // 42
  list_of(42)();      // 42

or the slightly more complex rule that the default constructor always  
returns an empty list and () only inserts after the list has been  
created:

Proposal 2:
  list_of<int>(42);   // 42
  list_of<int>()(42); // 42
  list_of<int>(42)(); // 42, 0
  list_of(42);        // 42
  list_of()(42);      // 42
  list_of(42)();      // 42, 0
  list_of<int>()();   // 0
  list_of()();        // 0

Michael.