Enhancement 7540 - Catch multiple exception types with single catch block

[yebblies]

Allow catching multiple exceptions with:

try { ... }
catch(auto e : E1, E2, E3)
{
}

http://d.puremagic.com/issues/show_bug.cgi?id=7540

[WalterBright]

fails autotester

[yebblies]

Conflicted with pull #737, should work now.

[MartinNowak]

tn and t could be the same. Maybe we could find a slightly better error message.

[yebblies]

Maybe "%s is listed more than once in catch list" or something. I don't like the normal wording much either. I hate coming up with error messages.

[MartinNowak]

How about the one from above. "catch of %s hides catch of %s" and "duplicate catch type %s".

[MartinNowak]

Looks good to me.

[yebblies]

Error messages improved.
Tuple expansion.
Now with slightly fewer ICEs!

[alexrp]

Do I understand this correctly? In your example, will e take on the common base type of E1, E2, and E3 (and error out if none exists (which, actually, shouldn't really happen, since we have Throwable...))?

[yebblies]

@alexrp That's the idea.

[andralex]

I don't think I'm behind this. There's some loss of type information, and the syntax is "surprising". I'd think a better approach is to define a multi-catch as a template that avoids repetition of source code while still preserving full type information. Even that I'm not sure whether it's a big enough improvement.

That being said, I recall another language (C#?) started supporting that recently.

[yebblies]

@andralex
The syntax is very easy to change.
Is preserving full type information actually useful? I would expect that if a specific exception type needs to be handled differently it would have it's own catch block.
Could you please elaborate on how the template version would be implemented and used?

[andralex]

@yebblies Whatever the syntax, the block controlled by catch should behave like a template parameterized on the exception type. Otherwise I feel this feature gives with one hand and takes with the other.

[yebblies]

I'm going to drop this as I have no plans to fix/maintain it in the near future.