Re: [boost] Re: unions

From: E. Gladyshev (egladysh_at_[hidden])
Date: 2003-10-07 03:05:08

--- Eric Friedman <ebf_at_[hidden]> wrote:

[...]

> 
> To check each type Ti in variant<T1,...,TN> would add O(n) compile-time 
> complexity. To check only the first type T1 adds only O(1) complexity.
> 
> In short, then, there's no theoretical reason to treat T1 specially, but 
> it seemed to me a good compromise.

I don't think that it is a good compromise.
It enables an unpredictable behaviour that is changing
based on the first type in the variant. 
If the user doesn't enforce the predictability
by using boost::empty, then all of her variant types
will behave differently based on what the first type is.
It is a very artificial and dangerous solution.

Eugene

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