Assert and the optional Message

[Jacob Carlborg]

On 2012-03-09 15:13, Timon Gehr wrote:
> On 03/09/2012 01:20 PM, Jacob Carlborg wrote:
>> On 2012-03-09 12:12, Jonathan M Davis wrote:
>>> On Friday, March 09, 2012 11:03:38 Regan Heath wrote:
>>>> On Fri, 09 Mar 2012 08:20:33 -0000, Chris Pons<cmpons at gmail.com> wrote:
>>>>> Any idea why, system("PAUSE") does work?
>>>>
>>>> As Jonathan says, assert throws AssertError... which means, if you
>>>> wanted
>>>> to you could catch it, for example...
>>>>
>>>> module asserting;
>>>>
>>>> import std.stdio;
>>>> import core.exception;
>>>>
>>>> debug
>>>> {
>>>> import std.c.windows.windows;
>>>> extern (C) int kbhit();
>>>> }
>>>>
>>>> void main()
>>>> {
>>>> try
>>>> {
>>>> assert(false, "testing assert");
>>>> }
>>>> catch(AssertError e)
>>>> {
>>>> debug
>>>> {
>>>> writefln("Assertion failed: %s", e);
>>>> writefln("Press any key to exit...");
>>>> while(!kbhit())
>>>> Sleep(1);
>>>> }
>>>> throw e;
>>>> }
>>>> }
>>>>
>>>> So, for debug builds your exe will output the assertion manually, and
>>>> wait
>>>> for a key press. Then re-throw the assertion (resulting in the d
>>>> runtime
>>>> outputting the assertion again). In release, no pause.
>>>>
>>>> Note: kbhit and Sleep are windows specific (sleep would be the unix
>>>> equivalent, not sure on one for kbhit).
>>>
>>> Bet advised that catching anything not derived from Exception is
>>> generally a
>>> _bad_ idea (most of which are derived from Error), and AssertError is
>>> _not_
>>> derived from Exception but rather Error. AssertErrors are not
>>> guaranteed to
>>> invoke finally blocks, scope statements, or destructors. Your program
>>> is in an
>>> invalid state when you catch an Error. So, while it may work in this
>>> particular case, it is _not_ something that you should be doing in
>>> general. By
>>> far the worst thing to do would be to catch an Error and then continue
>>> executing. Errors are _supposed_ to kill your program.
>>>
>>> - Jonathan M Davis
>>
>> Then I would say it's bad design to have "assert" throw an AssertError.
>> Whatever "assert" throws needs to be catchable, this is essential for
>> writing unit test frameworks. It needs to be possible to write a unit
>> test framework that catches all AssertErrors and prints a nice report at
>> the end (or similar).
>>
>
> This is a special case. Jonathan was specifically referring to the
> general case.

Then way is it an error? I still want it to call finally blocks, scope 
statements, and destructors.

-- 
/Jacob Carlborg