Re: [scope] Some random thoughts

From: Andrzej Krzemienski (akrzemi1_at_[hidden])
Date: 2023-12-02 22:31:08

sob., 2 gru 2023 o 22:20 Andrey Semashev via Boost <boost_at_[hidden]>
napisał(a):

> On 12/2/23 23:12, Andrzej Krzemienski via Boost wrote:
> > Hi All,
> > Two observations from reading the docs.
> >
> > Why do I need a condition in scope_exit when I have a scope_fail?
>
> There is a discussion about this in this section:
>
>
> https://lastique.github.io/scope/libs/scope/doc/html/scope/scope_guards.html#scope.scope_guards.condition_functions
>
> In short, scope_fail implies processing a failure event (for whatever
> definition of "failure") and scope_exit has no such connotation and can
> be used with arbitrary conditions. The different scope guards have
> different default conditions, too.
>

Having read the linked section as well as your reply, I still do not
understand the need for a scope_exit with a failure condition.
I either want to *always* call the callback function on scope exit, or only
under some condition. If it is under some condition, I would call
scope_failure or scope_success respectively.

Or are you saying that sometimes I want to call or skip the call based on
random conditions not having to do with failing anything, and where the
set_active would not work? Is that it? Do you have any convincing examples
for this?

> Internally, both scope_success and scope_fail are implemented on top of
> scope_exit and leverage its support for custom condition functions.
>

Ok, I get this part. I am just not sure if this is a sound design: because
I reused a pattern in the implementation, I will expose it to the users.

Regards,
&rzej;

>
> > I recommend putting warning somewhere in the docs that while using scope
> > guards you may inadvertently read an object after move:
> >
> > std::string checked(std::string name)
> > {
> >   scope::scope_exit g{[&]{
> >     std::clog << "checked " << name <<std::endl;
> >   }};
> >
> >   validate(name);
> >   return name; // name becomes moved-from
> > }
>
> Interesting observation, thanks.
>
>
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