Re: copying arrays

On Apr 29, 11:16 am, Q <qal...@xxxxxxxxx> wrote:
Hi all,

Simple question:

CL-USER 37 > (setf a (make-array 5 :initial-element 7))
#(7 7 7 7 7)

CL-USER 38 > (setf b a)
#(7 7 7 7 7)

CL-USER 39 > (eq a b)
T

CL-USER 40 > (setf (aref a 0) 9)
9

CL-USER 41 > a
#(9 7 7 7 7)

CL-USER 42 > b
#(9 7 7 7 7)

How do I pass copies of the array around, instead of the array
itself? I don't want them to be eq. But, it'd be nice if they were
equal :)
And then there's the problem - what if the array contains instances of
other arrays (or lists, or hashtables, or what not for that matter)?
Do you want to copy the member arrays? Or use the member array
directly? What if we have two arrays that happen to contain each
other?

In my experience it's quite rare to have to have to *copy* a
sequence. If you're manipulating an array, why would you want to
retain the previous version? What is it that you are trying to do?
In general, it is usually very rare that you have to actually copy the
sequence.

.

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