Re: More fun with slot type checking

According to the User's manual, defstructs do not have specialized slots for fixnums, but do have specialized slots for single-float's.  Hence, there's no check, I guess, on those fixnum slots.

Ray


 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Didier Verna
Sent: Monday, December 08, 2008 11:07 AM
To: CMU-CL Help
Subject: [cmucl-help] More fun with slot type checking


       Hi !

I'm continuing my experiments with slot type checking, on structures this time. Consider this:

(defstruct mystruct (slot "foo" :type single-float))

Regardless of the optimize settings, I will get an error every time I try to create a mystruct object; so it seems that CMU-CL performs structure slot type checking all the time.

However, in the following case:

(defstruct mystruct (slot "foo" :type fixnum))

I *never* get an error. I find this a bit inconsistent. Here's a wild guess that might explain this behavior: if it goes like in SBCL, fixnums are represented in structs in raw form, with their tag, so the consequence is that there is no need for any type checking[1] to guarantee that the slot can be accessed (read and written) properly, even with something else than a fixnum.

That would be different with single-float's if they use a specialized representation in structs, in which case you have to be more cautious when accessing the slot.

Comments ?



Footnotes: 
[1]  appart from honoring the user's type declaration of course

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