lisp - If strings are vectors, why are they immutable? -


if strings vectors of characters, , vector's elements can accessed using elt, , elt setf-able - why strings immutable?

strings not immutable in common lisp, mutable:

* last result lisp listener

cl-user 5 > (make-string 10 :initial-element #\-) "----------"  cl-user 6 > (setf (aref * 5) #\|) #\|  cl-user 7 > ** "-----|----"  cl-user 8 > (concatenate 'string "aa" '(#\b #\b)) "aabb"  cl-user 9 > (setf (aref * 2) #\|) #\|  cl-user 10 > ** "aa|b"

the thing should not modifying literal strings in code. consequences undefined. that's same issue other literal data.

for example file contains:

(defparameter *lisp-prompt* "> ")  (defparameter *logo-prompt* "> ")

if compile file compile-file, compiler might detect strings equal , allocate 1 string. might put them read-only memory. there other issues well.

summary

strings mutable.

don't modify literal strings in code.


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