toString should be final, it should do exactly what Sean is doing, return
file:line: msg, and I would say a stack trace as well.
msg should be a virtual property, and that's where someone can affect both
toString and the runtime printout.
So essentially, exactly what Andrei said, but s/toStringImpl/msg/
From Microsoft's Exception class (always good to look at what other languages
do):
"ToString returns a representation of the current exception that is intended to
be understood by humans. Where the exception contains culture-sensitive
data, the string representation returned by ToString is required to take into
account the current system culture. Although
there are no exact requirements for the format of the returned string,
it should attempt to reflect the value of the object as perceived by
the user.
The default implementation of ToString obtains the name of the class that threw
the current exception, the message, the result of calling ToString on the inner
exception, and the result of calling Environment.StackTrace. If any of these
members is Nothing, its value is not included in the returned string.
If
there is no error message or if it is an empty string (""), then no
error message is returned. The name of the inner exception and the
stack trace are returned only if they are not Nothing.
This method overrides Object.ToString."
-Steve
----- Original Message ----
From: Andrei Alexandrescu<[email protected]>
To: Discuss the phobos library for D<[email protected]>
Sent: Wed, April 7, 2010 2:39:20 PM
Subject: Re: [phobos] Printing exceptions
This seems to be an instance of the problem NVI is supposed to solve: the
interface for users should not be the same as the interface for
customization.
In an NVI approach, toString would be final and there
would be an overridable toStringImpl that users can tweak. Then toString would
call toStringImpl and decorate it with stack trace info etc.
Anyway,
since toString is already overridable, I suggest you just add a detailedReason()
function that formats and returns a string including whatever toString()
returns, then also file and line info and stack trace. If an exception leaves
main(), print detailedReason(), not toString().
Andrei
On
04/07/2010 01:09 PM, Sean Kelly wrote:
On Apr 7, 2010, at 8:53 AM,
Robert Clipsham wrote:
On 07/04/10 16:29, Sean Kelly
wrote:
The runtime can do one of two things: print exceptions
according to a standard format and inject the msg field in the proper place or
it can call toString. Which should be done? I prefer the former
because it makes for a standard presentation and doesn't risk allocating memory
needlessly, but I can see how people might do fancy stuff in toString that they
expect to be used instead. This came up because I'm adding a default stack
trace handler, and the current behavior prints the stack trace twice, so
something needs to change.
I think the better option
would be to print them in the standard format, at least by default. You could
always include several trace handlers to allow the user to effortlessly pick the
handler they want, rather than everyone implementing their own for when they
want to use toString.
My worry is that someone will do
something fancy in their toString override and expect it to print if the
exception escapes main(). The default behavior is basically to print
"file:line: msg" which sidesteps any custom code in toString completely.
The current code is actually a bit weird and uses the custom format if the file
string is non-null and calls toString otherwise, but that seems like it's even
less predictable than simply always using a custom or the toString format.
I also don't see any easy way to provide a default formatter, since ranges are
defined in Phobos and not druntime (ie. you couldn't have
Exception.outputTo(Range)).
I've personally never liked
toString, but since it exists it seems like the only reasonable thing to do is
always call it.
_______________________________________________
phobos mailing list
href="mailto:[email protected]";>[email protected]
http://lists.puremagic.com/mailman/listinfo/phobos
_______________________________________________
phobos
mailing list
href="mailto:[email protected]";>[email protected]
href="http://lists.puremagic.com/mailman/listinfo/phobos"; target=_blank
http://lists.puremagic.com/mailman/listinfo/phobos
_______________________________________________
phobos mailing list
[email protected]
http://lists.puremagic.com/mailman/listinfo/phobos
