Throwable class design

[rumbu]

On Friday, 1 February 2013 at 01:07:32 UTC, H. S. Teoh wrote:
> On Fri, Feb 01, 2013 at 01:47:35AM +0100, Andrej Mitrovic wrote:
>> On 2/1/13, Sean Kelly <sean at invisibleduck.org> wrote:
>> > I think the reason is mostly historic--the original exception
>> > classes had public members.  There's no reason why they 
>> > couldn't be
>> > hidden behind read-only properties though, other than the 
>> > potential
>> > to break existing code.
>> 
>> I'd rather we not, it's useful being able to modify msg and 
>> line
>> sometimes, e.g.:
>> http://forum.dlang.org/thread/uudharkmihxjymsxcyxq@forum.dlang.org#post-mailman.855.1359491827.22503.digitalmars-d-learn:40puremagic.com
>> 
>> Another example, wrapping `format` to inject the local file 
>> and line:
>> 
>> string fmt(string file = __FILE__, size_t line = __LINE__,
>> Args...)(string fmtStr, Args args)
>> {
>>     try
>>     {
>>         return format(fmtStr, args);
>>     }
>>     catch (FormatException exc)
>>     {
>>         exc.file = file;
>>         exc.line = line;
>>         throw exc;
>>     }
>> }
>> 
>> Saves me from having to read a broken stack trace or file and 
>> line
>> within Phobos.
>
> +1. Like this idea, I'll have to start using it to avoid the 
> headache of
> trying to figure out where something blew up when the 
> stacktrace points
> to some deep obscure code inside Phobos.
>
>
> T

I found this approach wrong, FormatException already contains 
useful information that you overwrite. The correct approach from 
my point of view is "throw new 
WhateverExceptionEvenFormatException("something wrong in fmt", 
file, line, exc)"; If Throwable was designed with encapsulation 
in mind, the code above was not be possible. Overwriting exc with 
new information will tell that the problem is in "fmt" not in 
"format".