body man page

itcl::body — change the body for a class method/proc

Synopsis

itcl::body className::function args body

Description

The body command is used outside of an [incr Tcl] class definition to define or redefine the body of a class method or proc. 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::function" identifies the method/proc being changed.

If an args list was specified when the function was defined in the class definition, the args list for the body command must match in meaning. Variable names can change, but the argument lists must have the same required arguments and the same default values for optional arguments. The special args argument acts as a wildcard when included in the args list in the class definition; it will match zero or more arguments of any type when the body is redefined.

If the body string starts with "@", it is treated as the symbolic name for a C procedure. The args list has little meaning for the C procedure, except to document the expected usage. (The C procedure is not guaranteed to use arguments in this manner.) If body does not start with "@", it is treated as a Tcl command script. When the function is invoked, command line arguments are matched against the args list, and local variables are created to represent each argument. This is the usual behavior for a Tcl-style proc.

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 body 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. The method bodies are included below the class definition via the body command. Note that the bodies of the constructor/destructor must be included in the class definition, but they can be redefined via the body command as well.

itcl::class File {
    private variable fid ""
    constructor {name access} {
        set fid [open $name $access]
    }
    destructor {
        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]
}

#
# See the File class in action:
#
File x /etc/passwd "r"
while {![x eof]} {
    puts "=> [x get]"
}
itcl::delete object x

Keywords

class, object, procedure

Info

3.0 itcl [incr Tcl]