在Elisp中深度复制字符串？

我有一个适当的字符串。我想对其进行深拷贝，以添加更多属性，同时将属性保留在原始字符串中。我该怎么做（轻松）？

例

一对一评估：

(setq test-str-1
      #(";; This `is' a test"
        0 3 (fontified nil face font-lock-comment-delimiter-face)
        3 9 (fontified nil face font-lock-comment-face)
        9 11 (fontified nil face (font-lock-constant-face font-lock-comment-face))
        11 19 (fontified nil face font-lock-comment-face)))
(setq test-str-2 (concat test-str-1))
(add-face-text-property 0 (length test-str-2) 'foobar t test-str-2)

结果：

test-str-2
;; =>
#(";; This `is' a test" 0 3 (fontified nil face (font-lock-comment-delimiter-face foobar))
  3 9 (fontified nil face (font-lock-comment-face foobar))
  9 11 (fontified nil face (font-lock-constant-face font-lock-comment-face foobar))
  11 19 (fontified nil face (font-lock-comment-face foobar)))
test-str-1
;; =>
#(";; This `is' a test" 0 3 (face font-lock-comment-delimiter-face fontified nil)
  3 9 (face font-lock-comment-face fontified nil)
  9 11 (face (font-lock-constant-face font-lock-comment-face foobar) ; <= foobar is here
        fontified nil)
  11 19 (face font-lock-comment-face fontified nil))

您可以使用该函数font-lock-append-text-property添加text属性。它不会破坏性地修改该值。

例如：

(setq test-str-1
      #(";; This `is' a test"
        0 3 (fontified nil face font-lock-comment-delimiter-face)
        3 9 (fontified nil face font-lock-comment-face)
        9 11 (fontified nil face (font-lock-constant-face font-lock-comment-face))
        11 19 (fontified nil face font-lock-comment-face)))
(setq test-str-2 (concat test-str-1))
(font-lock-append-text-property 0 (length test-str-2) 'face '(foobar t) test-str-2)


test-str-1
#(";; This `is' a test"
  0 3 (face font-lock-comment-delimiter-face fontified nil)
  3 9 (face font-lock-comment-face fontified nil)
  9 11 (face (font-lock-constant-face font-lock-comment-face) fontified nil)
  11 19 (face font-lock-comment-face fontified nil))

test-str-2
#(";; This `is' a test"
  0 3 (fontified nil face (font-lock-comment-delimiter-face foobar t))
  3 9 (fontified nil face (font-lock-comment-face foobar t))
  9 11 (fontified nil face (font-lock-constant-face font-lock-comment-face foobar t))
  11 19 (fontified nil face (font-lock-comment-face foobar t)))

在此，中的test-str-1保留了其原始值。

我发现可以通过遍历文本属性，复制基础属性数据并用新副本覆盖现有属性来做到这一点。

(defun deep-copy-text-properties (str)
  (with-temp-buffer
    (insert str)
    (goto-char 1)
    (while (not (eobp))
      (set-text-properties (point)
                           (goto-char (next-char-property-change (point) (point-max)))
                           ;; copy-tree is the important part
                           (copy-tree (text-properties-at (1- (point))))))
    (buffer-string)))

在我的测试中，这比您的read解决方案快20％。我还编写了一个不使用临时缓冲区的版本，并修改了代码较少但速度较慢的字符串属性。

查看C代码，它会复制属性plists，并使用copy_sequence来重建列表结构，但不会按值复制元素，因此示例中的face等具有列表值的属性将通过引用复制并修改。是否有错误，我不知道

您可以使用(concat the-original-string)。

例如：

(let ((s "TEXT"))
  (set-text-properties 2 3 '(:foreground "blue") s)
  (let ((q (concat s)))
    (add-text-properties 2 3 '(:background "red") q)
    (cons s q)))
;; Returns:
(#("TEXT" 2 3 (:foreground "blue")) . #("TEXT" 2 3 (:foreground "blue" :background "red")))

找到了一个（不是很有效的）解决方法：

(setq test-str-2
      (read (prin1-to-string test-str-1)))