tcl 数组问题 - 带引号的键

发布于 2024-10-14 13:31:29 字数 290 浏览 3 评论 0原文

这让我感到惊讶

>set foo("bar") 12
12
>parray foo
foo("bar") = 12
>set foo(bar) 12
12
>parray foo
foo("bar") = 12
foo(bar)   = 12

，似乎字面量 foo 与“foo”不同。然而

>string length foo
3
>string length "foo"
3

我还是不明白什么

原文

this surprised me

>set foo("bar") 12
12
>parray foo
foo("bar") = 12
>set foo(bar) 12
12
>parray foo
foo("bar") = 12
foo(bar)   = 12

it seems that the literal foo is not the same as "foo". And yet

>string length foo
3
>string length "foo"
3

what am I failing to understand

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蒗幽 2024-10-21 13:31:29

" 字符仅对 Tcl 的解析器来说是特殊的，位于单词的开头（或者当然是由 " 开头的单词的结尾）。事实上，如果您在其中添加空格，则会出现错误：

% set foo("b a r") 2
wrong # args: should be "set varName ?newValue?"

在执行 string length 调用的情况下，" 是在单词的开头，因此它很特殊。如果我们放置一个额外的前导垃圾字符，我们会发现 " 的特殊性消失了：

% string length x"bar"
6

如果您正在使用数组做一些复杂的事情。索引，我认为将元素的名称放入变量本身通常更容易，因为这样就更清楚发生了什么（并且通常也更容易调试）：

set idx "bar"
set foo($idx) 12

The " character is only special to Tcl's parser at the start of a word (or the end of a word that was started by ", of course). In fact, if you'd put spaces in you would have got an error:

% set foo("b a r") 2
wrong # args: should be "set varName ?newValue?"

In the case where you're doing the string length calls, the " is at the start of a word so it is special. If we put an extra leading junk character, we see that the specialness of " goes away:

% string length x"bar"
6

If you're doing something complicated with array indices, I think it's usually easier to put the name of the element in a variable itself, since then it's clearer what's going on (and usually easier to debug too):