Tcl/Tk的Switch模块中慎用注释

今天改了一段Tcl代码，一段非常复杂的非常长的swith代码，总是遇到这样一个奇怪的错误：

"extra switch pattern with no body, this may be due to a comment incorrectly placed outside of a switch body - see the "switch" documentation"

于是我检查{}是否匹配，检查entry写的是否正确，检查switch的变量是否正确……反复几遍之后，错误仍然在，几近崩溃。

Google了半天，也没找到解决方法。

最终还是抱着试试看的心态打开了Tcl/Tk经典书《Practical Programming in Tcl and Tk》，打开第六章第二节，发现本节结束处赫然写着这样一段话：

A comment can occur only where the Tcl parser expects a command to begin. This restricts the location of comments in a switch command.

You must put them inside the command body associated with a pattern, as shown in Example 6-6. If you put a comment at the same level as

the patterns, the switch command will try to interpret the comment as one or more pattern-body pairs.

该示例如下：

Example 6-6 Comments in switch commands
switch -- $value {
   # this comment confuses switch
   pattern { # this comment is ok }
}
 

我赶紧查看了一下我的代码，发现有好几个处“} ；#end of XXX”这样的注释。把它们去掉之后，就可以正常work了。

下面就是带有错误注释的不能工作的代码段。

                                         append C(HostMMCAP) ",$ap"
                                                # Record this reservd AP
                                                append MMCAPRSVD " $ap"
				        } ;# end of if
                                } else {
                                        AlertBox warn /
"You can NOT reserve it! This AP has been reserved by 
$rsv_login in $rsv_site with COOL session (COOLID) $rsv_id.

Please contact user /"$rsv_login/" if you really want to use it."
                                        set MMCAPDISPLAY($ap) 0
                                        return
                                } ;# end of else
                        } ;# end of entry "reserved"
 

由此得知，虽然“;#”这样的注释在Tcl中一般是很常见的，但是在switch中语句中是不能用的，只能在单独一行里写注释。

以此文为记。