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 BOOK Tcl/Tk Tools: contains an out of date tutorial for itcl.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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Lists both exported and private methods defined by CheckingAccountits ancestors, or mixins.
Constructors and destructors are also chained. Constructor and destructor method chains are only available through self callnot through info class call. Let us redefine the constructor for GeneralPurposeMixin.
So if we had a BrokerageAccount class or object, we could mix it in there as well. These tasks are performed through the special methods named constructor and destructor.
Within a method context, the command self call returns more or less the same information for the current object as info object call. The author uses mixed case for data members to avoid conflicts with names tutoial method arguments and local variables.
The unique namespace associated with the object is obtained through the self namespace command within a method context or with the info object namespace command elsewhere. This circular and self-referential relationship between oo:: This is a greatly simplified, not entirely accurate or correct, description for illustrative purposes.
You will see two output tuotrial in the above example. 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. No value judgement intended. These have subcommands that return different pieces of information about a class or an object. When the script passed to oo:: This creates a new class Account that can be used to create objects representing bank accounts.
The default implementation of this method, which is inherited by all objects from the root oo:: Let us rework our previous example.
Checking class membership You can get the class an object belongs to with info object class. Imagine our banking system had the requirement that individual accounts can be frozen based on an order from the tax authorities. The superclass command in the class definition establishes that SavingsAccount and CheckingAccount inherit from Account.
However, some OO systems layered on top of TclOO do offer this feature in a structured manner that does not explicitly expose internal object namespaces. It was intended to make programmers used to that language feel at home. Thus a checking account is a bank account and can be used at any place in the banking model where the behaviour associated with a bank account is expected.
The following code snippet will crash Tcl versions prior to 8. Thus in our banking example, we may define separate classes representing savings accounts and checking accounts, each inheriting from the base account and therefore having a balance and methods for deposits and withdrawal. We will not worry about how this is done but just assume some global procedures are available for the purpose.
In most languages, implementation of these messages involves calling methods which are just function calls with a context associated with the object. This means the object data members such as Balancedefined through variableare in the scope of the method and can directly be referenced without any qualifiers as seen in the method definition above.
From within the method context of an object, the command self class command returns the class defining the currently executing method. Thus the Log method is invoked twice, once before the withdraw method, and then again when that method in turn calls UpdateBalance. The class Account is actually just another Tcl command and could have been created in any namespace we choose, not necessarily the global one.
Perhaps most important, when implemented as a mixin, we can provide the feature sets to individual accounts, for example to specific savings accounts. You can help Wikipedia by expanding it.
Derived classes can define new data members using either variable in the class definition or my variable within a method as in withdraw. Note this is not necessarily the same as the class in which the filter method is defined.
This practice breaks encapsulation and is not recommended. Constructors and destructors There is one final thing we need to do 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. Ever since its introduction in the yeariTcl or incr Tcl has gone on to gain huge popularity among the Tcl Tk enthusiasts, and their development community.
For example, either oo:: 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.
Object-specific methods Let us illustrate with our banking example.
Conversely, the destructor method is run when the object is destroyed. Of course you can do the same with namespaces that’s what I’ve been doingbut it takes a lot more work, and the result isn’t as satisfying IMHO.
itcl – object-oriented extensions to Tcl – Linux Man Pages (n)
These differ from normal methods in only two respects: AMGApril Here we will simply illustrate with an example where we define a class hierarchy with multiple inheritance, mixins, filters and object-specific methods. The info class instances command returns a list of objects belonging to the specified class. Method definitions can be deleted at any time with the deletemethod command inside a class definition script. Usually though it is clear which one makes the most sense.
Design by Free web templates TclTk. This information can be obtained with the self next command from within a method context.
itcl (n) – Linux Man Pages
Some of these systems became fairly widely used and remain so today: Imagine we want to package some functionality as a mixin class. These are useful in programming dynamic object systems, runtime debugging and tracing, and building layered OO systems. When a state change occurs, the state machine object changes its class to the tjtorial corresponding to the target state.