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 BOOK Tcl/Tk Tools: contains an out of date tutorial for itcl.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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Further declarations will extend or modify the class behaviour. The question then arises as to what happens to objects that have already been created if a class is modified.

Imagine our banking system had the requirement that individual accounts can be frozen based on an order from the tax authorities. Rather, the constructor tutoriial is automatically run when an object is created.

So if we had a BrokerageAccount class or object, we could mix it in there as well. In the case of savings accounts, we only want select accounts to have this facility. Imagine writing a computer game where the characters are modeled as objects.

The info object call command returns a list that contains the method chain for a particular method invocation for a particular object. We can do it through introspection via the info object call command.

itcl (n) – Linux Man Pages

Not a problem, we can fix that by morphing the object to a CheckingAccount. Mixins versus inheritance Because one of its goal is to provide the required infrastructure for additional OO system to be built on top, TclOO offers a wide variety of capabilities that sometimes overlap in their effect. Data members do not have to be declared using variable in a class definition script. Let us illustrate with our banking example.


Between and there were over a dozen OO extensions for Tcl: Just like in that case a method tutoriql an arbitrary number of arguments including a variable number of trailing arguments collected as the args variable.

Let us create a class, Accountthat models a banking account.

Object Oriented Programming in Tcl

Tcl also provides the foundation for building extended OO systems on top. We will look at the contents of these definition scripts throughout this chapter, but for now, simply note that class definitions can be built up in incremental fashion. It then runs the first implementation in this list. For example, suppose instead of logging every transaction as in our earlier example, we only wanted to log withdrawals.

Constructors and destructors There is one final thing we need to ircl before we can start banking operations and that is to provide some means to initialize an Account object when it is created and perform any required clean up when it is destroyed. Options can be specified to control whether the list includes inherited and private methods.

The unknown method 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. Base method unknown unknown:: Thus a checking account is a bank account and can be used tuforial any place in the banking model where the behaviour associated with a bank account is expected.

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

The next command, which goes strictly by the order in the method chain, is not suitable in this case. Now we get a tutprial order to freeze Mr. The default implementation of this method, which is inherited by all objects from the root oo:: Lists both exported and private methods defined by CheckingAccountits ancestors, or mixins. The fact that they were defined through a class-level declaration is irrelevant. It would have been better to write the statement as.


Methods implemented via mix-ins appear in the method chain before methods defined on the object whereas inherited methods appear after. A good alternative is to automatically define accessor methods for public variables without the programmer having to explicitly do so.

Methods are defined through the method command which, like variableis executed as part of a class definition script. In most languages, implementation of these messages involves calling methods which are just function calls with a context associated with the object. Having defined our model, we can now begin operation of our bank to illustrate how objects are used. Method ttuorial can be changed by using the export and unexport commands inside a oo:: However, there is no requirement that filter methods must be private.

Why did we choose to go the mixin route? As it should be. These are however not discussed here. Let us see how all this works. This is detail as it maintains the same itcl programmer interface. Any method invocation on the object will then result in the filter method being invoked first.