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Subject: Re: [boost] [optional] generates unnessesary code for trivial types
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2012-02-14 14:53:34

Simonson, Lucanus J wrote:
> Hite, Christopher
> >Any C++ programmer reading your code should understand what
> > T* means. He may not be familiar with boost::optional<T&>.
> The real question is, is optional<T&> safer than T*? If
> someone accesses the object inside optional without checking
> if it is valid that is equivalent to dereferencing a pointer
> without checking if it is null. However, safety is about
> behavior, and people tend to dereference pointers without
> checking them very frequently because there are plenty of
> cases where it is safe to assume a pointer is not null.

I don't know to what "people" you're referring, but I check for null pointers before dereferencing them. If you want to pass the buck, always use smart pointers that validate dereferences. However, I prefer not to pay the overhead of checking for null on every dereference, so I convert to a reference once I've verified a non-null pointer, even with smart pointers, provided there's to be more than one dereference.

> In code review people ask me "why didn't you check if that
> pointer is null?" and my answer is usually, "because throwing
> an exception if it is null is the behavior I want". You

In that case, you're using a smart pointer.

> could say I should have used a reference instead, but it
> might not have been my pointer to start with.

What has that to do with it? Once I get a pointer into my code, I check for null, dereference it, and pass it by reference thereafter so no other code needs to test for null.

> Specifically, polymorphic data types are often passed around by
> pointer to base class instead of reference to base class by
> most C++ programmers.

Really? I'm certainly not "most C++ programmers" then. If something might not exist, I use optional or a pointer, depending. If it is required to exist, then I use a reference. I write functions taking references, not pointers, when I don't want to deal with the possibility of a null pointer. The caller must handle that for me.

Rob Stewart robert.stewart_at_[hidden]
Software Engineer using std::disclaimer;
Dev Tools & Components
Susquehanna International Group, LLP


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