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Loading incr-tcl into tclsh

If you're going to be using the Object Oriented extension to Tcl (Itcl), you may we working with a Tcl or tcl-based executable file that has it built in, or you may wish to load it in as a separate package. Many of the examples that you'll see in our training notes (and elsewhere) are designed for use with executables with [incr-Tcl] built in. So how can you use [incr-Tcl] otherwise?

[INCR-TCL]

What if you don't have an "itcl" executable, or you want to use [incr-Tcl] in association with a specific build of wish, expect or expectk that doesn't include the extra facilities?

earth-wind-and-fire:~/apr05 grahamellis$ tclsh
% source animal.itcl
invalid command name "class"
%

These days, [incr-Tcl] is supplied as a package with most distributions of Tcl and you can package require it to cause it to be loaded as necessary into the application. You'll then want to import the names from the namespace. Thus:

earth-wind-and-fire:~/apr05 grahamellis$ tclsh
% package require Itcl
3.3
% namespace import itcl::*
% source animal.itcl
% animal bill toucan 1.5
bill
% animal ben dog 6.2
ben
% ben getweight g
6200.0
% bill getweight lbs
0.681818181818
%

As an alternative, you could encapsulate the requirement for [incr-Tcl] within the sourced file so that the user's none the wiser that Itcl is being loaded. That is probably a better approach where you have a wide range of scripts being distributed to many machines and run through a variety of different executables.

FILE ANIMAL2.ITCL:

package require Itcl

itcl::class animal {
  variable breed
  variable weight
 constructor {b w} {
             set breed $b
            set weight $w
           }
       method getbreed {} {
            return $breed
           }
       method getweight {{units kgs}} {
                set w $weight
           if {$units == "g"} {set w [expr $w * 1000.0]}
           if {$units == "lbs"} {set w [expr $w / 2.2]}
            return $w
               }
       }

THE APPLICATION THAT CALLS THE ABOVE CLASS

#!/usr/bin/tclsh

# Example that loads Itcl into tclsh

puts "Hello - this is an Incr Tcl Demo"

source animal2.itcl

animal charlie cat 3.0
animal muppet dog 5.8

puts -nonewline "Charlie's weight (in pounds): "
puts [charlie getweight lbs]

puts -nonewline "Muppet's weight (in pounds): "
puts [muppet getweight lbs]

In operation:

earth-wind-and-fire:~/apr05 grahamellis$ ./petal
Hello - this is an Incr Tcl Demo
Charlie's weight (in pounds): 1.36363636364
Muppet's weight (in pounds): 2.63636363636
earth-wind-and-fire:~/apr05 grahamellis$


See also [incr-Tcl] training

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Related Material

Tcl/Tk - [incr-Tcl]
  [3142] Private and Public - and things between - (2011-01-22)
  [1925] Introduction to Object Oriented Programming - (2008-12-06)
  [1819] Calling base class constructors - (2008-10-03)
  [1528] Object Oriented Tcl - (2008-02-02)
  [656] Think about your design even if you don't use full UML - (2006-03-24)
  [290] Object Orientation in Tcl - [incr-Tcl] - (2005-04-24)

resource index - TclTk
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