Elisp：如何使用字符串键从关联列表中删除元素 [英] Elisp: How to delete an element from an association list with string key

问题描述

现在这样做很好：

(setq al '((a . "1") (b . "2")))
(assq-delete-all 'a al)

在我的应用程序中使用字符串作为键：

But I'm using strings as keys in my app:

(setq al '(("a" . "foo") ("b" . "bar")))

这样做无效：

(assq-delete-all "a" al)

我认为这是因为字符串对象实例是不同的（？）

I think that's because the string object instance is different (?)

那么我应该如何从关联中删除一个字符串键的元素清单？或者我应该放弃使用符号作为键，并在需要时将其转换为字符串？

So how should I delete an element with a string key from an association list? Or should I give up and use symbols as keys instead, and convert them to strings when needed?

推荐答案

如果你知道可以您只能在列表中单个匹配的条目，也可以使用以下格式：

If you know there can only be a single matching entry in your list, you can also use the following form:

(setq al (delq (assoc <string> al) al)

请注意， setq （您的示例代码中缺少）对列表上的删除操作非常重要，否则当已删除的元素恰好是列表中的第一个时，操作将失败。

Notice that the setq (which was missing from your sample code) is very important for `delete' operations on lists, otherwise the operation fails when the deleted element happens to be the first on the list.

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