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 BOOK Tcl/Tk Tools: contains an out of date tutorial for itcl.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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Note this is not the same as the class the object belongs to as the example below shows. You titorial claim ownership of the software; the authors and their institutions retain ownership, as described in the “license. Methods implemented via mix-ins appear in the method chain before methods defined on the object whereas inherited methods appear after.
As you can see, we have the same behaviour as before.
Object Oriented Programming in Tcl
Thus the above command will not show the variable Balance as that was defined in the base class Accountnot in SavingsAccount. Each may have additional functionality, for example check writing facilities for the checking account and interest payments for the savings account. Note the difference between the variable statement in the context of a class definition and the variable command used to define namespace variables.
The destructor method definition differs from other methods in that it only has a single parameter – the script to be run. Luckily, these tend to be few and far between so a couple of paragraphs is sufficient for this purpose. Each object is defined in one class file. The actual functionality is immaterial but it is intended to be fairly general purpose for example, logging or tracing and mixable into any class.
About iTcl or incr Tcl
Working with objects Tutroial defined our model, we can now begin operation of our bank to illustrate how objects are used. The list of methods that are set as filters can similarly be obtained with info class filters or info object filters. Note -clear option to clear any currently defined filters. The general thinking is that such classes are better modeled as mixins. Although not required in our example, it should be noted that variables defined in the class otcl not automatically visible in object-specific methods.
These differ from normal methods in only two respects: This is done with the command next which invokes the next method in the which in this case is the superclass method with the same name as the current method.
So the deposit method we saw earlier calls the UpdateBalance method as: Imagine our banking system had the requirement that individual accounts can be frozen based on an order from the tax authorities.
In that case we could have defined the Log command as follows:. This is a greatly simplified, not entirely accurate or correct, description for illustrative purposes. This information can be obtained with the self next command from within a method context. When called from within a oo:: Use of multiple inheritance is a somewhat controversial topic in OO circles. The first command returns an empty list because no variables were declared through variable for that object. One of these design choices involves mixins and inheritance.
Method definitions can be deleted at any time with the deletemethod command inside a class definition script.
The created objects are Tcl commands and as such can be created in any namespace. Luckily, we do not have to work it out while reading the manpage. As you see, a method is defined in exactly the same manner as proc defines a Tcl procedure.
In Dec,on comp. Objects and classes The core of OO programming is, no surprise, an object. For these reasons, mixins seemed a better choice in our design aside from the fact that we needed some example to illustrate mixins.
Object Oriented Programming in Tcl
You can use, copy, modify and even redistribute this software without any written agreement or royalty, provided that you keep all copyright notices intact. Notice that the EFT class does not really know anything about accounts.
Defining a filter class The filter declaration need not occur in the same class that defines the filter method. However, deletion of methods from objects is sometimes useful in specialization of objects.
As it should be.
Inheritance The ircl characteristic of OO systems is support for inheritance. The object would respond to messages to deposit or withdraw funds. However, some OO systems layered on top of TclOO do offer this feature in a structured manner that does not explicitly expose tjtorial object namespaces. 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.
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Since we want all checking accounts to have this facility, we will add EFT to the CheckingAccount class as a mixin. TclOO can be used as a standalone OO system by itself. Not directly inheriting or modifying the CheckingAccount class was a no-brainer for obvious reasons.