Tcl/Tk：使用带有 expr 的数组
我在尝试访问 expr 内的 array 时遇到问题。重现错误的代码如下所示，改编自 Donal Fellows 对我的 之前的问题。
namespace eval Ns {
}
proc Ns::main_routine {} {
global cb
array set cb {
c1 0
c2 0
c3 0
c4 0
}
checkbutton .c1 -text "C1" -variable cb(c1)
checkbutton .c2 -text "C2" -variable cb(c2)
checkbutton .c3 -text "C3" -variable cb(c3)
checkbutton .c4 -text "C4" -variable cb(c4)
grid .c1 -sticky w
grid .c2 -sticky w
grid .c3 -sticky w
grid .c4 -sticky w
# _After_ initializing the state...
trace add variable cb(c1) write Ns::reconfigureButtons
trace add variable cb(c2) write Ns::reconfigureButtons
trace add variable cb(c3) write Ns::reconfigureButtons
trace add variable cb(c4) write Ns::reconfigureButtons
}
proc Ns::reconfigureButtons args {
global cb
# this one works
set state "normal"
if { $cb(c1) } {
set state "disabled"
}
.c2 configure -state $state
# this one does not
#.c2 configure -state [expr $cb(c1) ? "disabled" : "normal"]
#.c4 configure -state [expr $cb(c1)||$cb(c3) ? "disabled" : "normal"]
}
Ns::main_routine
我想修复上面代码中的以下行
.c2 configure -state [expr $cb(c1) ? "disabled" : "normal"]
当我使用上面的行时，出现以下错误：
can't set "cb(c1)": invalid bareword "disabled" in expression "1?disabled :正常”;
I am running into problems while trying to access array inside an expr. The code which reproduces the error is shown below which is adapted from Donal Fellows answer to my earlier question.
namespace eval Ns {
}
proc Ns::main_routine {} {
global cb
array set cb {
c1 0
c2 0
c3 0
c4 0
}
checkbutton .c1 -text "C1" -variable cb(c1)
checkbutton .c2 -text "C2" -variable cb(c2)
checkbutton .c3 -text "C3" -variable cb(c3)
checkbutton .c4 -text "C4" -variable cb(c4)
grid .c1 -sticky w
grid .c2 -sticky w
grid .c3 -sticky w
grid .c4 -sticky w
# _After_ initializing the state...
trace add variable cb(c1) write Ns::reconfigureButtons
trace add variable cb(c2) write Ns::reconfigureButtons
trace add variable cb(c3) write Ns::reconfigureButtons
trace add variable cb(c4) write Ns::reconfigureButtons
}
proc Ns::reconfigureButtons args {
global cb
# this one works
set state "normal"
if { $cb(c1) } {
set state "disabled"
}
.c2 configure -state $state
# this one does not
#.c2 configure -state [expr $cb(c1) ? "disabled" : "normal"]
#.c4 configure -state [expr $cb(c1)||$cb(c3) ? "disabled" : "normal"]
}
Ns::main_routine
I want to fix the following line in the above code
.c2 configure -state [expr $cb(c1) ? "disabled" : "normal"]
When I use the above line I get the following error:
can't set "cb(c1)": invalid bareword "disabled" in expression "1? disabled : normal";
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评论（2）
您应该始终在表达式周围放置
{大括号}，因为这样会停止双重替换，而将"引号"保留为做他们正确的目的。通过这样做，您还可以提高代码的安全性和速度，并且至少从 Tcl 8.0 开始（十多年前）就已经这样做了；在此之前，出于性能原因，许多人省略了大括号，但这确实是一个可怕的习惯。简而言之，不要使用：
而是使用这个：
You should always put
{braces}around expressions, as that stops double substitution, leaving the"quotes"to do their proper purpose. You also boost the security and speed of your code by doing that, and have done since at least Tcl 8.0 (over a decade ago); before that, performance reasons meant that many people omitted braces, but that was a truly terrible habit.In short, don't use:
But rather use this:
你尝试过吗
.c2 配置-状态 [expr {$cb(c1) ? “禁用”：“正常”}]Did you try
.c2 configure -state [expr {$cb(c1) ? "disabled" : "normal"}]