itcl User Commands - body






NAME

     body - change the body for a class method/proc


SYNOPSIS

     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  "imple-
     mentation"  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 register-
     ing  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.

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

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




KEYWORDS

     class, object, procedure