configbody(3itcl)
NAME
configbody - change the "config" code for a public variable
SYNOPSIS
itcl::configbody className::varName body _________________________________________________________________
DESCRIPTION
The configbody command is used outside of an [incr Tcl] class
definition to define or redefine the configuration code associated with
a public variable. Public variables act like configuration options for
an object. They can be modified outside the class scope using the
built-in configure method. Each variable can have a bit of "config"
code associate with it that is automatically executed when the variable
is configured. The configbody command can be used to define or
redefine this body of code.
Like the body command, this facility allows a class definition to have
separate "interface" and "implementation" parts. The "interface" part
is a class command with declarations for methods, procs, instance
variables and common variables. The "implementation" part is a series
of body and configbody commands. If the "implementation" part is kept
in a separate file, it can be sourced again and again as bugs are
fixed, to support interactive development. When using the "tcl" mode
in the emacs editor, the "interface" and "implementation" parts can be
kept in the same file; as bugs are fixed, individual bodies can be
highlighted and sent to the test application.
The name "className::varName" identifies the public variable being
updated. If the body string starts with "@", it is treated as the
symbolic name for a C procedure. Otherwise, it is treated as a Tcl
command script.
Symbolic names for C procedures are established by registering
procedures via Itcl_RegisterC(). This is usually done in the
Tcl_AppInit() procedure, which is automatically called when the
interpreter starts up. In the following example, the procedure
My_FooCmd() is registered with the symbolic name "foo". This procedure
can be referenced in the configbody command as "@foo".
int
Tcl_AppInit(interp)
Tcl_Interp *interp; /* Interpreter for application. */
{
if (Itcl_Init(interp) == TCL_ERROR) {
return TCL_ERROR;
}
if (Itcl_RegisterC(interp, "foo", My_FooCmd) != TCL_OK) {
return TCL_ERROR;
}
}
EXAMPLE
In the following example, a "File" class is defined to represent open
files. Whenever the "-name" option is configured, the existing file is
closed, and a new file is opened. Note that the "config" code for a
public variable is optional. The "-access" option, for example, does
not have it.
itcl::class File {
private variable fid ""
public variable name ""
public variable access "r"
constructor {args} {
eval configure $args
}
destructor {
if {$fid != ""} {
close $fid
}
}
method get {}
method put {line}
method eof {}
}
itcl::body File::get {} {
return [gets $fid]
}
itcl::body File::put {line} {
puts $fid $line
}
itcl::body File::eof {} {
return [::eof $fid]
}
itcl::configbody File::name {
if {$fid != ""} {
close $fid
}
set fid [open $name $access]
}
#
# See the File class in action:
#
File x
x configure -name /etc/passwd
while {![x eof]} {
puts "=> [x get]"
}
itcl::delete object x
KEYWORDS
class, object, variable, configure
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