Emacs如何确定撤消的工作单位 [英] How Emacs determines a unit of work to undo

问题描述

当您输入命令 C - / 时，Emacs将撤消您最近对缓冲区进行更改的一部分。当您再次输入 C - / 时，它会撤消另一个工作。

When you enter the command C-/, Emacs undoes some part of your recent changes to a buffer. When you enter C-/ again, it undoes another chunk of work.

我已经阅读了，但它的确是如何工作的，这是模糊的。该手册说连续字符插入命令通常被分组在一个单个撤销记录，但它并不解释如何决定构成组的字符插入命令的数量。一个组中的字符数似乎是随机的。

I have read the Emacs manual entry on Undo but it is vague about exactly how it works. The manual says "Consecutive character insertion commands are usually grouped together into a single undo record" but it does not explain how it decides the number of character insertion commands that constitute a group. The number of characters it puts in a group seems random.

任何人都可以解释Emacs用于将字符分组到撤销记录中的算法？

Can anyone explain the algorithm Emacs uses to group characters into undo records?

推荐答案

设置撤消边界的逻辑主要在 self-insert-command = http://bzr.savannah.gnu.org/lh/emacs/trunk/annotate/head:/src/cmds.c> cmds.c 。您必须阅读完整故事的代码，但基本上：

The logic for setting undo boundaries is mostly in self-insert-command which is implemented in cmds.c. You'll have to read the code for the full story, but basically:

• 只要输入字符，就会有一个撤消边界每20个字符你输入。


• 但是，如果你发出一个不同的编辑命令（例如杀死一个字），这将导致立即添加一个撤消边界，重置字符数


• 某些毛茸茸的插入（由 internal_self_insert 确定）会立即添加一个撤消边界，并且字符数复位。阅读代码，看起来好像是：（1）在覆盖模式中，如果你用一个具有不同宽度的字符，例如在标签上打字（2）如果插入的字符导致缩写被扩展; （3）如果您键入的字符导致 auto-fill-mode 插入缩进。


• 此外，任何编辑命令撤销边界可以通过调用 undo-boundary 来请求它是一个好主意。这不会导致字符数被重置。

• As long as you are just typing characters, there's an undo boundary every 20 characters you type.
• But if you issue a different editing command (you kill a word, for example), this causes an undo boundary to be added immediately, resetting the character count.
• Certain "hairy" insertions (as determined by internal_self_insert) cause an an undo boundary to be added immediately, and the character count to be reset. Reading the code, it looks as though these are: (1) in overwrite-mode, if you overwrote a character with one that has a different width, e.g. typing over a tab; (2) if the character you inserted caused an abbreviation to be expanded; (3) if the character you typed caused auto-fill-mode to insert indentation.
• In addition, any editing command that decides it would be a good idea to have an undo boundary can request it by calling undo-boundary. This does not cause the character count to be reset.

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