The Right Approach to Exceptions

[Nick Sabalausky]

"Nick Sabalausky" <a at a.a> wrote in message 
news:jhu61p$1jpm$1 at digitalmars.com...
> "Andrei Alexandrescu" <SeeWebsiteForEmail at erdani.org> wrote in message 
> news:jhtss8$12mq$3 at digitalmars.com...
>> On 2/20/12 10:16 AM, Nick Sabalausky wrote:
>>> "Andrei Alexandrescu"<SeeWebsiteForEmail at erdani.org>  wrote in message
>>> news:jhtq31$u8q$1 at digitalmars.com...
>>>>
>>>> Again, I think this thread clarified we need the "Variant[string] 
>>>> info;"
>>>> member however we define the hierarchy.
>>>>
>>>
>>> I disagree. I don't see a need for that.
>>
>> How would we address custom formatting of e.g. error messages?
>>
>
> Maybe I've misunderstood your intent for this "Variant[string] info;" My 
> understanding is that, for example, you want to replace this:
>
> ----------------------------------------------------
> class Exception {}
> class FooException
> {
>    string fooName;
>    int fooID;
>    bool didBarOccur;
>
>    this(string fooName, int fooID, bool didBarOccur)
>    {
>        this.fooName = fooName;
>        this.fooID= fooID;
>        this.didBarOccur= didBarOccur;
>    }
> }
> ----------------------------------------------------
>
> With this:
>
> ----------------------------------------------------
> class Exception
> {
>    Variant[string] info;
> }
> class FooException
> {
>    string fooName;
>    int fooID;
>    bool didBarOccur;
>
>    this(string fooName, int fooID, bool didBarOccur)
>    {
>        this.fooName = fooName;
>        this.fooID= fooID;
>        this.didBarOccur= didBarOccur;
>
>        info["fooName"] = fooName;
>        info["fooID"] = fooID;
>        info["didBarOccur"] = didBarOccur;
>    }
> }
> ----------------------------------------------------
>
> If so, then I don't see any usefulness of "Variant[string] info" other 
> than to start treating exceptions like JS's abomination of an "object" (Or 
> at least AS2's objects anyway - not 100% certain how much of AS2 is taken 
> from JS). If not, then could you clarify what you meant?
>
> In either case, I am interested to hear in more detail how you see 
> "Variant[string] info" being used to address i18n. I haven't really dealt 
> with a lot of i18n myself.
>

Ok, I just saw your explanation here: 
http://forum.dlang.org/post/jhu1hk$1cb8$1@digitalmars.com

And, IIUC, I assume that inside "stringTemplate()", you'd then access some 
table that roughly amounts to (yea, I know we don't have 2D AAs):

string[string, Locale] i18nTable;
i18nTable["FileNotFoundExcepton", English] = "File ${filename} not found";

Then stringTemplate() would look that up, find the string "File ${filename} 
not found" and essentially do:

return "File "~e.info("filename")~" not found";

Although obviously not hardcoded like that.

Is that right?

In that case, I like the general idea, *but* why not just use reflection to 
access the members instead of essentially creating a JS-style "class" with 
AAs? That way we don't have to either A. throw away the benefits that class 
members have over AAs or B. violate DRY by duplicating field members in an 
AA.