Re: [boost] [smart_ptr] Interest in the missing smart pointer (that can target the stack)

Subject: Re: [boost] [smart_ptr] Interest in the missing smart pointer (that can target the stack)
From: Rob Stewart (rob.stewart_at_[hidden])
Date: 2016-02-04 05:45:30

On February 2, 2016 9:20:11 PM EST, Noah <duneroadrunner_at_[hidden]> wrote:
> On 2/2/2016 1:40 AM, Rob Stewart wrote:
> 
> using the garbage value might be dangerous in some contexts.
> 
> Yeah, you're right. But how rare are those contexts? I mean it's not 
> rare for an integer to be used as an index into an array.
> 
> If you're saying that you agree with the decision to enforce mandatory
> default initialization of std::vectors, but uninitialized construction
> is ok for integers because the most catastrophic consequences would 
> happen a lower percentage of the time, I dunno, it seems to me this 
> argument is a judgement call that depends on how much lower that 
> percentage is, and the magnitude of the real world benefits of
> foregoing default initialization.

It's a lot simpler than that: Trust the Programmer. That's been part of C and C++ from the start. By all means default construct with zero-initialization and provide a converting constructor from numeric types. That will provide the safety you're after. However, rather than prevent a not uncommon use case, just make that use case possible.

[snip example of latent bug using native integer]

> So ideally what I would like is for boost to provide a set of types
> that 
> when used in lieu of the regular C++ types, ensure that the code is 
> deterministic. Or as deterministic as possible. Because being 
> deterministic increases the value and effectiveness of testing.

Of course.

> > Adding a separate class or policy just to have the
> > uninitialized case is heavy, but the overload may not apply to all
> > specializations of the template.
> 
> Yeah, I'm not sure either. Separate classes does seem heavy. But at 
> least it's compile-time heavy, not run-time.

I meant that users have to know about more types and how to select among them or infer a programmer's intent from their use. 

> Anyway I wonder if this is all moot. Have you looked at all at the
> "safe 
> numerics" library proposed in this newsgroup? The post from Jan 20 has
> links. That library seems use a template to generate classes of "safe"
> integers or whatever.

I have. I alluded to those when I mentioned the idea that your classes should do more for conversions, etc.

___
Rob

(Sent from my portable computation engine)