Import Tcl 8.6.12

pkgs/itcl4.2.2/doc/code.n

@@ -0,0 +1,94 @@
+'\"
+'\" Copyright (c) 1993-1998  Lucent Technologies, Inc.
+'\"
+'\" See the file "license.terms" for information on usage and redistribution
+'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
+'\"
+.TH code n 3.0 itcl "[incr\ Tcl]"
+.so man.macros
+.BS
+'\" Note:  do not modify the .SH NAME line immediately below!
+.SH NAME
+itcl::code \- capture the namespace context for a code fragment
+.SH SYNOPSIS
+\fBitcl::code \fR?\fB-namespace \fIname\fR? \fIcommand \fR?\fIarg arg ...\fR?
+.BE
+
+.SH DESCRIPTION
+.PP
+Creates a scoped value for the specified \fIcommand\fR and its
+associated \fIarg\fR arguments.  A scoped value is a list with three
+elements:  the "\fC@scope\fR" keyword, a namespace context,
+and a value string.  For example, the command
+.CS
+namespace foo {
+    code puts "Hello World!"
+}
+.CE
+produces the scoped value:
+.CS
+@scope ::foo {puts {Hello World!}}
+.CE
+Note that the \fBcode\fR command captures the current namespace
+context.  If the \fB-namespace\fR flag is specified, then the
+current context is ignored, and the \fIname\fR string is used
+as the namespace context.
+.PP
+Extensions like Tk execute ordinary code fragments in the global
+namespace.  A scoped value captures a code fragment together with
+its namespace context in a way that allows it to be executed
+properly later.  It is needed, for example, to wrap up code fragments
+when a Tk widget is used within a namespace:
+.CS
+namespace foo {
+    private proc report {mesg} {
+        puts "click: $mesg"
+    }
+
+    button .b1 -text "Push Me" \
+        -command [code report "Hello World!"]
+    pack .b1
+}
+.CE
+The code fragment associated with button \fC.b1\fR only makes
+sense in the context of namespace "foo".  Furthermore, the
+"report" procedure is private, and can only be accessed within
+that namespace.  The \fBcode\fR command wraps up the code
+fragment in a way that allows it to be executed properly
+when the button is pressed.
+.PP
+Also, note that the \fBcode\fR command preserves the integrity
+of arguments on the command line.  This makes it a natural replacement
+for the \fBlist\fR command, which is often used to format Tcl code
+fragments.  In other words, instead of using the \fBlist\fR command
+like this:
+.CS
+after 1000 [list puts "Hello $name!"]
+.CE
+use the \fBcode\fR command like this:
+.CS
+after 1000 [code puts "Hello $name!"]
+.CE
+This not only formats the command correctly, but also captures
+its namespace context.
+.PP
+Scoped commands can be invoked like ordinary code fragments, with
+or without the \fBeval\fR command.  For example, the following
+statements work properly:
+.CS
+set cmd {@scope ::foo .b1}
+$cmd configure -background red
+
+set opts {-bg blue -fg white}
+eval $cmd configure $opts
+.CE
+Note that scoped commands by-pass the usual protection mechanisms;
+the command:
+.CS
+@scope ::foo {report {Hello World!}}
+.CE
+can be used to access the "foo::report" proc from any namespace
+context, even though it is private.
+
+.SH KEYWORDS
+scope, callback, namespace, public, protected, private