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What namespace is used to evaluate commands or access variables for a Tk widget?

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What namespace is used to evaluate commands or access variables for a Tk widget?
posted May 15, 2014 by Anshika Utadi

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1 Answer

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Ordinary variable names and code fragments are evaluated in the global namespace. This is consistent with vanilla Tcl/Tk, and provides backward-compatibility with existing Tcl/Tk applications.

Consider the following example:

  proc show {mesg} {
        puts "global: $mesg"
    }
    namespace foo {
        variable x
        proc show {mesg} {
            puts "foo: $mesg"
        }
    checkbutton .cb -variable x -command {show "state = $x"}
}

The checkbutton .cb is created within namespace ::foo. However, its -variable and -command options are ordinary strings, and they are evaluated in the global namespace. The name "x" refers to the variable "::x", and the command "show" refers to "::show".

If a widget is meant to use commands and variables in the local namespace, it must be configured with scoped values as follows:

namespace foo {
    .cb configure \
        -variable [scope x] \
        -command [code {show "state = $x"}]
}
answer May 16, 2014 by Samardeep Acharya
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