The Right Approach to Exceptions

Ben Davis entheh at
Sat Feb 18 17:10:10 PST 2012

On 18/02/2012 21:07, Andrej Mitrovic wrote:
> On 2/18/12, Nathan M. Swan<nathanmswan at>  wrote:
>> It would be nice if there was a mixin template that creates an
>> exception class that acts like this; making similar exception
>> classes is annoying.
> It would be even nicer if we didn't need a mixin for classes that
> simply forward the ctor call to the base class ctor:
> class FileException : Exception { }   // no-go, have to write a ctor
> that forwards to super
> AIUI this has something to do with ctors not being virtual. I think
> someone mentioned this could be improved one day.

I guess this is a bit off topic, but what you probably want is syntactic 
sugar that says "declare constructors matching all super constructors 
and calling through to them" and can be used in ANY class hierarchy (not 
necessarily exceptions). For example:

class Subtype : Supertype {
     super all;

If you want to expose just specific constructors, then there could also 
be a shorthand for "declare a constructor matching a specific super 
constructor and calling through to it" - so you don't have to repeat all 
the arguments. For example:

class Subtype : Supertype {

That would then make it an entirely separate issue and completely not 

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