1code(n) [incr Tcl] code(n)
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8 itcl::code - capture the namespace context for a code fragment
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11 itcl::code ?-namespace name? command ?arg arg ...?
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16 Creates a scoped value for the specified command and its associated arg
17 arguments. A scoped value is a list with three elements: the "@scope"
18 keyword, a namespace context, and a value string. For example, the
19 command
20 namespace foo {
21 code puts "Hello World!"
22 }
23 produces the scoped value:
24 @scope ::foo {puts {Hello World!}}
25 Note that the code command captures the current namespace context. If
26 the -namespace flag is specified, then the current context is ignored,
27 and the name string is used as the namespace context.
28 Extensions like Tk execute ordinary code fragments in the global names‐
30 pace. A scoped value captures a code fragment together with its names‐
31 pace context in a way that allows it to be executed properly later. It
32 is needed, for example, to wrap up code fragments when a Tk widget is
33 used within a namespace:
34 namespace foo {
35 private proc report {mesg} {
36 puts "click: $mesg"
37 }
38 button .b1 -text "Push Me" -command [code report "Hello World!"]
40 pack .b1
41 }
42 The code fragment associated with button .b1 only makes sense in the
43 context of namespace "foo". Furthermore, the "report" procedure is
44 private, and can only be accessed within that namespace. The code com‐
45 mand wraps up the code fragment in a way that allows it to be executed
46 properly when the button is pressed.
47 Also, note that the code command preserves the integrity of arguments
49 on the command line. This makes it a natural replacement for the list
50 command, which is often used to format Tcl code fragments. In other
51 words, instead of using the list command like this:
52 after 1000 [list puts "Hello $name!"]
53 use the code command like this:
54 after 1000 [code puts "Hello $name!"]
55 This not only formats the command correctly, but also captures its
56 namespace context.
57 Scoped commands can be invoked like ordinary code fragments, with or
59 without the eval command. For example, the following statements work
60 properly:
61 set cmd {@scope ::foo .b1}
62 $cmd configure -background red
63 set opts {-bg blue -fg white}
65 eval $cmd configure $opts
66 Note that scoped commands by-pass the usual protection mechanisms; the
67 command:
68 @scope ::foo {report {Hello World!}}
69 can be used to access the "foo::report" proc from any namespace con‐
70 text, even though it is private.
71
74 scope, callback, namespace, public, protected, private
75itcl 3.0 code(n)