如何使用三元运算符向 tcl 中的匿名字符串添加可选部分? [英] How do I use the ternary operator to add an optional part to an anonymous string in tcl?

问题描述

我是 tcl 的新手(对不起，如果答案很明显，但阅读教程和文档没有帮助).我在 tcl 中有一个声明:

I am new to tcl (sorry if the answer is obvious, but reading tutorials and documentation did not help). I have a statement in tcl that says:

startupitem.start "foo
\tbar"

我想做的是让foo"部分成为可选的，这取决于结果[variant_isset "alice"] 使用三元运算符而不使用变量.

What I would like to do is have the "foo" part become optional, depending on the outcome of [variant_isset "alice"] using the ternary operator and without using variables.

我已经尝试了几件事

startupitem.start "[variant_isset """alice"""?"""foo\n\t""":""""""] bar"

(当然有各种转义和组合或在双引号内使用双引号)但我没有成功.

(of course with all kinds of escapes and combo's or the use of the double quotes inside the double quotes) but I haven't succeeded.

如果 variant_isset 表达式返回 true 的结果是它等价于

The outcome if the variant_isset expression returns true is that it is equivalent to

startupitem.start "bar" 

推荐答案

您想查看 Tcl 的 expr 命令，它引入了 Tcl 的表达式子语言 incl.你称之为三元"运算符?:

You want to check out Tcl's expr command, which introduces Tcl's expression sub-language incl. what you call the "ternary" operator ?:

startupitem.start "[expr {[variant_isset "alice"] ? "foo\n\t" : ""}]bar"

如果您碰巧最近使用了 Tcl，您可能更喜欢使用 string cat，而不是就地:

If you happen to use a Tcl recent enough, you may want to prefer an outplace string assembly using string cat, rather than inplace:

string cat [expr {[variant_isset "alice"] ? "foo\n\t" : ""}] "bar"

这篇关于如何使用三元运算符向 tcl 中的匿名字符串添加可选部分?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！