configbody(3itcl)

NAME
itcl::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_RegisterObjC(). 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_FooObjCmd() 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_RegisterObjC(interp, "foo", My_FooObjCmd) != 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