Re: [ALACPP] Chris' stupid C++ trick of the week

["Jon Stewart" <stew1@xxxxxxxxxxx>]

> So, this is a little off the core purpose of this list, but I thought
> I'd share a C++ tidbit.


I'd say this is quite on-topic.


> template<typename T>
> T& doFoo(T& aTarget) {
>     //do something with aTarget
>     return aTarget;
> }

...

> The object referenced by aBar may be destroyed when you exit the doFoo()
> block (and obviously before the caller gets a chance to look at it).
> How? Well, the compiler actually has the option of passing arguments to
> doFoo() by value. Of course this is only in the special case of a
> parameter passed as a ref to a const.


I didn't know compilers were allowed to do that. It seems patently broken.

Someone needs to rant at Bjarne about that.


> 1) Use compile time assertions to ensure that the template is not
> instantiated on const types.
> 
> 2) Make sure Bar's copy constructor is private, and better still with
> pure virtual functions which will cause a linker error in the event that
> you get by the privacy restriction.
> 
> 3) Use a typelist to limit the types which my generic function can take
> to a select set of non-const types.
> 
> 4) Use a compiler that always inlines templated function calls. ;-)


Well, I'd prefer specifying the function as inline. It's not guaranteed to 
work -- compilers always have the option of not-inlining -- but... I'd bet 
most of them would take you at your word, especially for a template 
function.

Otherwise you could be lame and change the function signature to be:

doFoo(T *foo)

Pointers are cheesy, but they work (unlike references).



Jon
-- 
Jon Stewart
stew1@xxxxxxxxxxx
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