Re: narrowing conversions with arrays

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From: John Wood (spam_at_isannoying.com)
Date: 04/15/04 

Date: Thu, 15 Apr 2004 21:00:19 GMT

ok slight confusion, sorry.
   Base[] bases = new Base[1];
   bases[0] = new Inherited();
   inheriteds = (Inherited[])bases;

Causes the runtime error. You changed it to:
   Base[] bases = new Inherited[1];
   bases[0] = new Inherited();
   inheriteds = (Inherited[])bases;

Which does work.

So the compiler doesn't raise an error because bases can contain an instance
of an array of any type derived from Base -- and the compiler doesn't know
which particular instance it contains.

Makes sense....

Learnt something else while playing with this... the following code produces
this exception:

An unhandled exception of type 'System.ArrayTypeMismatchException' occurred
Attempted to store an element of the incorrect type into the array.

  class Base { }
  class Base2 : Base { }
  class Inherited : Base { }

  Base[] bases;
  Inherited[] inheriteds;

  Base[] bases = new Inherited[1];
  bases[0] = new Base2();
  inheriteds = (Inherited[])bases;

"Jon Skeet [C# MVP]" <skeet@pobox.com> wrote in message
news:MPG.1ae9025c1d406b0598a6c1@msnews.microsoft.com...
> John Wood <spam@isannoying.com> wrote:
> > What ver of .net are you running?
> > When I run the code on 1.0 it causes a runtime error. Perhaps it's fixed
in
> > 1.1.
>
> It's certainly fine on 1.1, but I'm surprised it fails on 1.0. What
> error are you getting? Are you running the *exact* code I posted?
>
> --
> Jon Skeet - <skeet@pobox.com>
> http://www.pobox.com/~skeet
> If replying to the group, please do not mail me too

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