'\"
'\" 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.
'\"
'\" RCS: $Id: configbody.n,v 1.1 1998/07/27 18:41:59 stanton Exp $
'\"
.so man.macros
.TH configbody n 3.0 itcl "[incr\ Tcl]"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
configbody \- change the "config" code for a public variable
.SH SYNOPSIS
\fBconfigbody \fIclassName\fB::\fIvarName body\fR
.BE

.SH DESCRIPTION
.PP
The \fBconfigbody\fR command is used outside of an \fB[incr\ Tcl]\fR
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 \fBconfigure\fR method.
Each variable can have a bit of "config" code associate with it
that is automatically executed when the variable is configured.
The \fBconfigbody\fR command can be used to define or redefine
this body of code.
.PP
Like the \fBbody\fR command, this facility allows a class definition
to have separate "interface" and "implementation" parts.
The "interface" part is a \fBclass\fR command with declarations
for methods, procs, instance variables and common variables.
The "implementation" part is a series of \fBbody\fR and
\fBconfigbody\fR 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 \fBemacs\fR 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.
.PP
The name "\fIclassName\fB::\fIvarName\fR"
identifies the public variable being updated.
If the \fIbody\fR string starts with "\fB@\fR", it is treated
as the symbolic name for a C procedure.  Otherwise, it is
treated as a Tcl command script.
.PP
Symbolic names for C procedures are established by registering
procedures via \fBItcl_RegisterC()\fR.  This is usually done
in the \fBTcl_AppInit()\fR procedure, which is automatically called
when the interpreter starts up.  In the following example,
the procedure \fCMy_FooCmd()\fR is registered with the
symbolic name "foo".  This procedure can be referenced in
the \fBconfigbody\fR command as "\fC@foo\fR".
.CS
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;
    }
}
.CE

.SH 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.
.CS
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 {}
}

body File::get {} {
    return [gets $fid]
}
body File::put {line} {
    puts $fid $line
}
body File::eof {} {
    return [::eof $fid]
}

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]"
}
delete object x
.CE

.SH KEYWORDS
class, object, variable, configure
