[lldb-dev] LLDB Evolution - Final Form

[Zachary Turner via lldb-dev]

On Tue, Sep 20, 2016 at 1:55 PM Greg Clayton <gclayton at apple.com> wrote:

>
> > On Sep 20, 2016, at 1:45 PM, Zachary Turner <zturner at google.com> wrote:
> >
> > I do agree that asserts are sometimes used improperly.  But who's to say
> that the bug was the assert, and not the surrounding code?  For example,
> consider this code:
> >
> > assert(p);
> > int x = *p;
>
> Should be written as:
>
> assert(p);
> if (!p)
>     do_something_correct();
> else
>     int x = *p;
>
> >
> > Should this assert also not be here in library code?  I mean it's
> obvious that the program is about to crash if p is invalid.  Asserts should
> mean "you're about to invoke undefined behavior", and a crash is *better*
> than undefined behavior.  It surfaces the problem so that you can't let it
> slip under the radar, and it also alerts you to the point that the UB is
> invoked, rather than later.
> >
> > What about this assert?
> >
> > assert(ptr);
> > int x = strlen(ptr);
> >
> > Surely that assert is ok right?  Do we need to check whether ptr is
> valid EVERY SINGLE TIME we invoke strlen, or any other function for that
> matter?  The code would be a disastrous mess.
>
> Again, check before you call if this is in a shared library! What is so
> hard about that? It is called software that doesn't crash.
>
> assert(ptr)
> int x = ptr ? strlen(ptr) : 0;
>

I find it hard to believe that you are arguing that you cannot EVER know
ANYTHING about the state of your program.  :-/

This is like arguing that you should run a full heap integrity check every
time you perform a memory write, just to be sure you aren't about to crash.


If you make a std::vector<>, do we need to verify that its internal pointer
is not null before we write to it?   Probably not, right?  Why not?
Because it has a specification of how it works, and it is documented that
you can construct one, you can use it.

It's ok to document how functions work, and it is ok to assume that
functions work the way they claim to work.
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