Nevin ":-]" Liber wrote:
Please go back to the top and reread my rule of thumb (with Marshall's addendum, which I agree with and use).
You mean this: My general rule of thumb is that if mucking with ownership or lifetime, pass a smart pointer. If not, pass a raw pointer. Again, I disagree. Did you think I didn't read it and didn't know what I was disagreeing with? Marshall's addendum, to which I replied, also doesn't change it for me and relies, as the basis of its argument, on what I believe is questionable design decisions.
In other words, code written like that is fragile and should be used sparingly.
Exactly. That's why I disagree. I prefer not to have fragile code,
where the caller has to "be careful" (which is merely a euphemism for "be perfect", as any mistake creates a subtle bug).
Exactly why I disagree with your "rule of thumb".
If you a way of passing a raw pointer or reference where it is always safe for the called function to copy and use that pointer or reference later without any external guarantees about the lifetime of the object pointed/referred to, I'd certainly be interested in hearing about it.
The fact that there is none is why I disagree. At least a reference advertises the fact that you certainly should not be keeping a copy. So use a shared pointer or other RAII device when a reference is inappropriate...as a general rule of thumb. By using a pointer you are already, "mucking with ownership issues." Even if the answer to those issues is, "This function will not keep this pointer." So I think that your rule of thumb and the reasoning behind it are flawed. I can see when such is necessary given other constraints, for you'll never be able to get code perfect by all measures, but I do not like the idea of using it as a rule of thumb. If you see a pointer and you are not asking what the ownership semantics of that pointer are, I'd say you're neglecting to consider a potentially very large problem. Furthermore, your general rule of thumb is going to kick you in the face once you start mixing pointers gained and lost through other APIs such as wxWidgets, where passing a pointer into a function can be disowning it. When your general rule of thumb is, "Avoid raw pointers," you can separate that which you've created from these other libraries by simply documenting that any raw pointer, unless otherwise commented, is owned by that library. Your rule of thumb seems arbitrary to me, fails to address the ownership issue, and balances precariously upon the understanding of other developers in the face of competing paradigms. I don't think I like it.