plucky (3) configbody.3itcl.gz

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