From: David Abrahams (dave_at_[hidden])
Date: 2003-10-08 17:14:56
"E. Gladyshev" <egladysh_at_[hidden]> writes:
> --- David Abrahams <dave_at_[hidden]> wrote:
>> Sorry to be so blunt, but that's just crazy. Without the basic
>> guarantee, any program invariant is allowed to be disrupted by an
>> exception, and recovery is impossible.
> I don't get what you mean. I can always handle exceptions
> on my own just like in case of typical class or C style union
> types. What is so special about variant?
Nothing at all. The basic guarantee is just about the minimum
required for exception recovery with *any* component.
> What is program invariant?
>> > Even if you decide to support basic guarantees, why do you need the
>> > heap backup and first-type based switch?
>> Because of variant's invariant: "thou shalt always contain a value of
>> one of your types".
> Who said that?
It's part of variant's spec.
"Boost.Variant guarantees the type of its content is one of a
finite, user-specified set of types"
It would be nice if this invariant were made more explicit in the
-- Dave Abrahams Boost Consulting www.boost-consulting.com
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