Re: [boost] [optional] Specializing optional to save space

Subject: Re: [boost] [optional] Specializing optional to save space
From: Nevin Liber (nevin_at_[hidden])
Date: 2015-09-27 16:38:56

On 27 September 2015 at 15:03, David Stone <david_at_[hidden]> wrote:

> Andrzej posted another thread about creating a new compact_optional class.
> The goal of this class is to make it easy to create a new optional type
> with a special sentinel value. This allows easy customization per instance
> of an optional value.
>
> This post is about the opposite approach: making it easier to specialize
> optional to provide special behavior for all instances of a given optional
> type.
>
> When I bring this up, people often compare it to the vector<bool>
> specialization, but this is a completely different issue.

No, it's the same issue.  It'll have subtly different behavior.  Generic
programming counts on the behavior being the same.

The only reason vector<bool> is bad is because of its spelling.  Had it
been a different name, most people would be happy.

optional<T> controls the lifetime of T.  If you have a sentinel instead,
then the lifetime of the engaged T is exactly the same as the lifetime of
optional<T>.

If you want a type with different behavior, give it a different name.
-- 
 Nevin ":-)" Liber  <mailto:nevin_at_[hidden]>  [phone]