Eliminate some gratuitous string mutation

* lisp/play/zone.el (zone-replace-char):
* lisp/international/quail.el (quail-get-translations):
* lisp/hippie-exp.el (he-capitalize-first): Clarify the code by removing
mutation that is probably not resizing but just in case.

lisp/hippie-exp.el

@@ -334,11 +334,12 @@ undoes the expansion."
 
 (defun he-capitalize-first (str)
   (save-match-data
-    (if (string-match "\\Sw*\\(\\sw\\).*" str)
-	(let ((res (downcase str))
-	      (no (match-beginning 1)))
-	  (aset res no (upcase (aref str no)))
-	  res)
+    (if (string-match "\\Sw*\\(\\sw\\)" str)
+	(let ((b (match-beginning 1))
+              (e (match-end 1)))
+          (concat (substring str 0 b)
+                  (upcase (substring str b e))
+                  (downcase (substring str e))))
       str)))
 
 (defun he-ordinary-case-p (str)

lisp/international/quail.el

@@ -2135,10 +2135,14 @@ minibuffer and the selected frame has no other windows)."
     (let ((guidance (quail-guidance)))
       (if (listp guidance)
 	  ;; We must replace the typed key with the specified PROMPT-KEY.
-	  (dotimes (i (length str))
-	    (let ((prompt-key (cdr (assoc (aref str i) guidance))))
-	      (if prompt-key
-		  (aset str i (aref prompt-key 0)))))))
+          (setq str (apply #'string
+                           (mapcar
+                            (lambda (c)
+	                      (let ((prompt-key (assq c guidance)))
+	                        (if prompt-key
+		                    (aref (cdr prompt-key) 0)
+                                  c)))
+                            str)))))
 
       ;; Show followable keys.
       (if (and (> (length quail-current-key) 0) (cdr map))

lisp/play/zone.el

@@ -433,8 +433,9 @@ run a specific program.  The program must be a member of
 
 (defsubst zone-replace-char (count del-count char-as-string new-value)
   (delete-char (or del-count (- count)))
-  (aset char-as-string 0 new-value)
-  (dotimes (_ count) (insert char-as-string)))
+  (let ((s (apply #'propertize (string new-value)
+                  (text-properties-at 0 char-as-string))))
+    (dotimes (_ count) (insert s))))
 
 (defsubst zone-park/sit-for (pos seconds)
   (let ((p (point)))