Re: [boost] A nonnewable class

From: Milutin Jovanovic (miki_at_[hidden])
Date: 2000-08-22 08:03:45

From: "David Abrahams" <abrahams_at_[hidden]>
> 1. noncopyable can be used when no sensible copy semantics exist. There is
> simply no analogue for dynamic construction. If it makes sense to write
>     X x;
> then it also makes sense to say
>    std::auto_ptr<X> x(new X);

Until recently I did not see much use for it, but we have a concrete example
in our thread conversations. The mutex_lock class that locks a mutex only
within a scope should not be allowed to exist on heap and that way keep the
lock outside of scopes. Object stored in your auto_ptr can very legaly
survive past the end of your scope.

> 2. noncopyable prevents copying even when the type in question is a
> subobject. nonnewable can't prevent dynamic allocation as a subobject.

True, but the writer of the subclass takes responsibility for that. Yes, it
opens a door for workarounds, but at least you warned (strongly) the user.

Cheers,

Miki Jovanovic.