[dmd-internals] Asserts

[Walter Bright]

On 11/9/2012 10:10 PM, David Held wrote:
> Relying on the debugger to tell you where something went wrong is pretty 
> ghetto, IMO.  For instance, the debugger makes all of the commented-out 
> printfs() in the code also redundant, and yet I see thousands of these.  So 
> which is it...should the compiler give you diagnostic information, or should 
> you rely on the debugger?  Since we're on this topic, let's then switch it to 
> the nature of diagnostics in dmd.

I'll often use printf because although the debugger knows types, it rarely shows 
the values in a form I particularly need to track down a problem, which tends to 
be different every time. And besides, throwing in a few printfs is fast and 
easy, whereas setting break points and stepping through a program is an awfully 
tedious process. Or maybe I never learned to use debugger properly, which is 
possible since I've been forced to debug systems where no debugger whatsoever 
was available - I've even debugged programs using an oscilloscope, making clicks 
on a speaker, blinking an LED, whatever is available.

Note that getting a call stack for a seg fault does not suffer from these 
problems. I just:

    gdb --args dmd foo.d

and whammo, I got my stack trace, complete with files and line numbers.


>
> Since I work on apps professionally that need to be running 24/7, I am 
> naturally inclined to rely on logging rather than debugging.

> Especially when there may be hundreds of instances running, while only a few 
> actually experience a problem, logging usually turns out to be the better 
> choice.  Then consider that logging is also more useful for bug reporting, as 
> well as visualizing the code flow even in non-error cases.

Sure, but that doesn't apply to dmd. What's best practice for one kind of 
program isn't for another.

>
> One of my TODO items was to take the commented-out printfs and turn them into 
> a first-class logging solution with configurable log levels/modules/etc. (so 
> you can turn on logging in just one subsystem if you want).  If the reigning 
> philosophy is instead to lean on the debugger, then that would be a waste of 
> time.  What do y'all think?

I've tried that (see the LOG macros in template.c). It doesn't work very well, 
because the logging data tends to be far too voluminous. I like to tailor it to 
each specific problem. It's faster for me, and works.