[patch][google/integration] Add lightweight checks to vector::begin et. al. (issue4973065)

[Paul Pluzhnikov]

On Tue, Sep 6, 2011 at 1:33 PM, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:

>>  for (it = v->begin(); it != v->end(); ++it)  // Oops!
>
> Eurgh, the occurrence of "delete" in anything except a destructor is a
> code smell that should have led someone to find those bugs anyway!
> Obviously the code above is a trivial example, but it's unforgivable
> to write that

I can assure you that the actual code that exhibited these bugs was much
subtler than that, and the bugs were not immediately obvious.

Sometimes they were not immediately obvious even after running Valgrind
on the buggy code and getting allocation/deletion/access stack traces with
source corrdinates.

>> We can't (easily) catch the general problem. This patch allows us to easily
>> catch this particular instance of it.
>
> Sure, but so does adding "assert(this);" at the top of every member

Sorry, no. Adding "assert(this);" does not catch any new bugs (at least
not on Linux) -- the code would have immediately crashed on zero-page
dereference anyway.

Thanks,
-- 
Paul Pluzhnikov