[boost] Re: [variant] 2 or more types requirement

From: Eric Friedman (ebf_at_[hidden])
Date: 2003-02-23 01:33:44

Ronald Garcia wrote:
> In reading through the variant docs, I noticed a requirement that at least
> two types must be supported by the variant.  Is this meant for ease of
> library implementation, or is this a means of protecting programmers from
> themselves? :-)
[snip]

In addition to the comments offered by Itay, the original idea was that one
parameter would be reserved exclusively for the variant<Types> syntax. With
the advent of mpl::is_sequence, however, this is no longer necessary IMO.

Now, particularly after proposals for the idea of variant containing an
empty 'void' type, I am in favor of eliminating the parameter count
requirement altogether. In other words, variant<> would be shorthand for
variant<void>, which would be always empty but still conformant with the
variant interface.

Thanks for your comments.

Eric