Re: [boost] compressed_pair initialization

From: John Maddock (john_at_[hidden])
Date: 2006-05-19 05:36:43

David Abrahams wrote:
> I find myself creating this class member:
>
>      compressed_pair<
>          storage
>        , compressed_pair<
>              Lookup
>            , compressed_pair<
>                  GetUnstored
>                , SetUnstored
>              >
>          >
>      > members;

Just one comment here: shouldn't the storage member be in the innermost 
compressed_pair?  Currently the innermost item compressed_pair<GetUnsorted, 
SetUnsorted> has two empty members and so isn't actually "compressed".

Using:

compressed_pair<
    empty1,
    compressed_pair<
        empty2,
        compressed_pair<
            empty3,
            storage> > >

ensures that each compressed pair has one non-empty member and one empty 
member, so the final object should be just sizeof(storage).

All of which suggests that a compressed-tuple would be a good idea, although 
ordering the items within the tuple to ensure compression is actually a 
larger challenge than folks may have realised.

In the mean time if additional template constructors can be added, I see no 
problem with that.

John.