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 Forum index » DIY Hardware and Software » ChucK programming language
Latest mystery problem
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chuckles



Joined: Apr 02, 2007
Posts: 72
Location: San Diego, California

PostPosted: Mon Jun 04, 2007 9:53 am    Post subject: Latest mystery problem
Subject description: Bug?
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OK, here's a simple demonstration of something that gives a compile error that I can't figure out. Mandolin and StifKarp are both StkInstruments, yes?

Then why do these statements compile OK:

Code:
[new StifKarp, new Mandolin ] @=> StkInstrument voice1;

[]; [new Mandolin, new StifKarp ] @=> StkInstrument voice2[];


but these give an error message

Code:
[new StifKarp, new StifKarp ] @=> StkInstrument voice3[];

[new Mandolin, new Mandolin ] @=> StkInstrument voice4[];


Code:
[unnamed2]:line(7): cannot assign '@=>' on types 'Mandolin[]' @=> 'StkInstrument[]'...
[unnamed2]:line(7): ...(reason: --- incompatible types for assignment)


This can be extended too to more than two instruments. I found out about it by experimenting with the "In C" project where he defines something like 9 instruments which are a mixture of StifKarp and Mandolin. I wondered why he did that and it's apparently because you can't create an array of StkInstruments that are all the same type.

Comments, anyone?

Thanks!

c.
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spencer



Joined: Aug 16, 2006
Posts: 53
Location: northern california

PostPosted: Mon Jun 04, 2007 4:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey chuckles,
I think ChucK's implicit typing rules force a literal array of objects to be the most specific type/subclass possible while still having them be all the same type at some level. So
Code:
[new StifKarp, new Mandolin ] @=> StkInstrument voice1;
is an array of StkInstruments, but
Code:
[new StifKarp, new StifKarp ] @=> StkInstrument voice3[];
is an array of StifKarps. Also, unfortunately, ChucK's typing rules don't allow you to cast an array of a class to an array of its superclass.

Anyways the solution is this:
Code:
[new Mandolin $ StkInstrument, new Mandolin ] @=> StkInstrument voice4[];
This forces ChucK to think that the most specific type that applies to all elements is StkInstrument, so it is an array of StkInstrument rather than Mandolin.

spencer
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chuckles



Joined: Apr 02, 2007
Posts: 72
Location: San Diego, California

PostPosted: Tue Jun 05, 2007 8:26 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks so much Kassan, that will make life easier for me, and it also educates me about $ casting...

(Another way to get around the problem, apparently, though not very elegant, would be to explicitly assign like:

Code:
StkInstrument voice4[2];

new StifKarp @=> voice4[0];
new Mandolin @=> voice4[1];
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Kassen
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Joined: Jul 06, 2004
Posts: 7678
Location: The Hague, NL
G2 patch files: 3

PostPosted: Tue Jun 05, 2007 9:35 am    Post subject: Reply with quote  Mark this post and the followings unread

chuckles wrote:
Thanks so much Kassan,


I'm happy you are happy but (Spencer != Kassen), in fact I haven't yet had the pleasure of meeting Spencer in person.

There's more then one person trying to answer question in the ChucK-scene(and that's a good thing too!).

:¬)

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chuckles



Joined: Apr 02, 2007
Posts: 72
Location: San Diego, California

PostPosted: Fri Jun 08, 2007 8:34 am    Post subject: Reply with quote  Mark this post and the followings unread

My apologies to both Spencer and Kassen; Spencer for not thanking him for his clarification of my problem, and Kassen for spelling his name wrong! Thanks to both of you for helping out in this forum -- the forest of ChucK has some dark areas and mysterious paths for a beginner...

...c...
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Kassen
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Joined: Jul 06, 2004
Posts: 7678
Location: The Hague, NL
G2 patch files: 3

PostPosted: Fri Jun 08, 2007 9:23 am    Post subject: Reply with quote  Mark this post and the followings unread

No harm done, Chuckles. I've had a unusual name for quite a while now and I've been dyslexic for a similar period so i can't blame anyone for spelling.

And, yes, it does, but I think that's half the fun.

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