Make Exception a class, not an interface, and remove the const constructor.

Make Exception a class, not an interface, and remove the const constructor.

We should consider removing the constructor entirely, there is never a good excuse for throwing a non-descript Exception. If you do, it should likely be an Error instead.

Committed: https://code.google.com/p/dart/source/detail?r=15077

[Lasse Reichstein Nielsen, 2012-11-14 15:24:18]

For committing when we can break things again.

[floitsch, 2012-11-14 15:43:22]

LGTM.

https://codereview.chromium.org/11369243/diff/1/sdk/lib/core/exceptions.dart
File sdk/lib/core/exceptions.dart (right):

https://codereview.chromium.org/11369243/diff/1/sdk/lib/core/exceptions.dart#...
sdk/lib/core/exceptions.dart:20: String toString() => (message == null) ?
"Exception" : "Exception: $message";
safeToString?

[Bob Nystrom, 2012-11-14 18:02:39]

https://codereview.chromium.org/11369243/diff/1/sdk/lib/core/exceptions.dart
File sdk/lib/core/exceptions.dart (right):

https://codereview.chromium.org/11369243/diff/1/sdk/lib/core/exceptions.dart#...
sdk/lib/core/exceptions.dart:20: String toString() => (message == null) ?
"Exception" : "Exception: $message";
Nit, but I would prefer it if "Exception: " were not included in the string. We
have to hack around that manually in pub to give nice user-friendly error
messages:
http://code.google.com/p/dart/source/browse/branches/bleeding_edge/dart/utils...

[Lasse Reichstein Nielsen, 2012-11-16 08:21:01]

I would actually prefer to make Exception completely abstract and not give it a
default implementation.

Exceptions are for domain-specific exceptional cases. It's intended to be caught
by a user and used, not just printed before the program dies. Using "new
Exception('foo')" is really doing it wrong - it gives no information to the user
catching it, it's just a generic "something went wrong". The only reason for
having a default Exception implementation is to help people hacking together
prototype code until they get around to creating the real Exception class (but
that use-case is actually reasonable enough to reluctantly keep the
implementation around).

If you expect a specific message to be included, use a specialized Exception
class. Please do that anyway. 
We have code that throws plain Exception. That code should be changed (some of
them probably to Errors).

[Lasse Reichstein Nielsen, 2012-11-16 08:22:48]

https://codereview.chromium.org/11369243/diff/1/sdk/lib/core/exceptions.dart
File sdk/lib/core/exceptions.dart (right):

https://codereview.chromium.org/11369243/diff/1/sdk/lib/core/exceptions.dart#...
sdk/lib/core/exceptions.dart:20: String toString() => (message == null) ?
"Exception" : "Exception: $message";
It should be a String, but better safe than sorry.

[sra1, 2012-11-16 08:31:32]

On 2012/11/16 08:21:01, Lasse Reichstein Nielsen wrote:
> I would actually prefer to make Exception completely abstract and not give it
a
> default implementation.
> 
> Exceptions are for domain-specific exceptional cases. It's intended to be
caught
> by a user and used, not just printed before the program dies. Using "new
> Exception('foo')" is really doing it wrong - it gives no information to the
user
> catching it, it's just a generic "something went wrong". The only reason for
> having a default Exception implementation is to help people hacking together
> prototype code until they get around to creating the real Exception class (but
> that use-case is actually reasonable enough to reluctantly keep the
> implementation around).

Please keep the ability to do this.  I've learned a lot by adding debug "throw
new Exception('hi');" at various places.  I guess I could just throw a string.

> 
> If you expect a specific message to be included, use a specialized Exception
> class. Please do that anyway. 
> We have code that throws plain Exception. That code should be changed (some of
> them probably to Errors).

Yes, I think a style-level warning would be appropriate.

[Lasse Reichstein Nielsen, 2012-11-19 13:18:53]

https://codereview.chromium.org/11369243/diff/1/sdk/lib/core/exceptions.dart
File sdk/lib/core/exceptions.dart (right):

https://codereview.chromium.org/11369243/diff/1/sdk/lib/core/exceptions.dart#...
sdk/lib/core/exceptions.dart:20: String toString() => (message == null) ?
"Exception" : "Exception: $message";
Seems some tests expect the exact output that we currently have. We should fix
those too eventually, and perhaps use safeToString, but not now.
I moved safeToString to Error, since it seems generally useful. It used to be in
NoSuchMethodError.