Abbreviated form of incr Tcl, iTcl is the term used for referring to the object- oriented extensions meant for Tcl programming language. Let’s learn more about . The name is often written as “itcl” as that contains no metacharacters (i.e., space or brackets). BOOK Tcl/Tk Tools: contains an out of date tutorial for itcl. A more tutorial introduction is presented in the paper included with this distribution. See the class command for more details on creating and using classes.

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Now let us define another class that also uses the mixin.

Object Oriented Programming in Tcl

The following code accomplishes this. The class Account is actually just another Tcl command and could have been created in any namespace we choose, not necessarily the global one.

Defining data members In our simple example, the state for an account object includes an account number that uniquely identifies it and the current balance. The home page is http: Lifecycle Object Generators describes an ifcl of when such morphing might be used. Or even modified or derived from the CheckingAccount class to add transfer methods.

This is-a relation is key when deciding whether to use ifcl or some other facility such as mix-ins.

itcl (n) – Linux Man Pages

As seen above, the self filter command returns a list of three items: Another point about method definitions concerns method visibility. Lists both exported and private methods defined by CheckingAccountits ancestors, or mixins.

So the deposit method we saw earlier calls the UpdateBalance method as: Obj81 saving account data to database. Constructor and destructor method chains are only available through self callnot through info class call.

The latter invokes the next method in the method chain while the former only tell you what the next method is. The returned list contains two interesting elements: This can be useful for example when tutorila are used to segregate objects. A private method on the other hand, can only be invoked from within another method in the object context. It was one of the earliest Tcl-based OO extensions to be widely used.


The unknown method is passed the name of the invoked method as its first argument followed by the arguments from the invocation tutoril. When might you use this? To start with a clean slate, let us get rid of the Log method we defined on the object earlier. Enumerating classes Classes are also objects in TclOO and therefore the same tutoria, used to enumerate objects can be used to enumerate classes.

TclOO provides facilities to support both the classy and the classless [ 1 ] models.

Classes are also objects in TclOO and therefore the same command used to enumerate objects can be used to enumerate classes. Every object has a method named unknown which is run when no method of that name is defined for that object actually in the method chain for that object as we see later. Now we get a court order to freeze Mr.

The advantage of course is that defining a class allows a collection of additional behaviours to be abstracted and easily added to any class or object without repeating the code. Just like Tcl, iTcl also has built-in support for easy integration of the C based codes into the iTcl classes. Notice that the EFT class does not really know anything about accounts.

From a method context, the self call command returns similar titorial while self next identifies the next method implementation in the chain.

Inspecting method chains within method contexts Within a method context, the command self call returns more or less the same information for the current object as info object call. Each object is defined in one class file. What sets a mix-in apart is the conceptual model and how the class is used. In fact, the potential specialization includes features such as forwarding, filters and mix-ins but we leave them for now as we have not discussed them as yet.


We could specialize every method for his accounts via oo:: This defines the data members for the class as per-object variables. The question then arises as to what happens to objects that have already been created if a class is modified.

Further we have mixins for both a class and directly into the object. Method chains Throughout this chapter we have seen that when a method is invoked on an object, the code implementing the method for that object may come from several different places – the object, its class or an ancestor, a mixin, forwarded methods, filters or even unknown method handlers.

[incr Tcl] – Object-Oriented Programming in Tcl/Tk

The nextto command allows this control. Object Orientation for TclFellows et al, http: The method context also makes available several commands – such as selfnext and my – which can only be called from within a method. Notice from the output that all method invocations, even those called internally from deposit are recursively logged. They need to be brought into scope with the my variable statement. Its Web presence may not always be up to date, but the code base in CVS is.

The filter declaration need not occur in the same class that defines the filter method. Inheritance refers to the ability of a derived class also refered to as a subclass to specialize a class – called its base class or superclass – by extending or modifying its behaviour. What does the method chain look like for a method that is not defined for the object?

Let us illustrate with our banking example. Filter methods are bypassed when invoking constructors, destructors or the unknown method of a class.