This seems very dangerous to me - perhaps you should consider not using this.

[This is used frequently - someone want to explain why and when it is needed?]

Isn't this just the Itcl counterpart to namespace code ?

GWM The namespace code page says that it is a constructor for namespace inscope; inscope says "This command is not expected to be used directly by programmers". Thus I would expect that itcl::code should also not be used by (end user) programmers, although the construct might be used in supplied Tcl packages. The purpose of declaring a variable 'private' is to assure the programmer that there can be no unexpected modifications of the variable other than through the class interface methods.

APW My use of itcl::code is when I have a callback for example for a widget and I want to execute that callback in the "environment" of an itcl class method even if that method is not public. That normally means, that I also install the callback from within that "environment".

GWM I would think that any callback should be a public member as it is being accessed from outside the class (via the event handler). Here is my short example of creating a class which creates a button and handles its callbacks. Each button is a separate object and can be extended to carry any other data specific to that button's callback. Note that the callback command must be in "" so that the parameter $this is substituted at the object/callback creation time.

  package require Itcl
  itcl::class hellobtn {
    public variable name "No-one"
    constructor {{frame ""}} { 
        pack [ button $frame.hbtn -text "Hello World" -command "$this greet $frame.hbtn" ]
    }

    method greet {btn} { $btn config -background red -text $name        }
  }
  foreach btn {"Don't" Press This Button} {
        pack [frame .f$btn]
          hellobtn h$btn .f$btn
        h$btn configure -name "$btn"
  }