Smalltalk
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| - | Dissatisfied with relational or [[OOP]] mappings of the real world? Let's create | + | Dissatisfied with relational or [[OOP]] mappings of the real world? Let's create a better world inside a computer! Let's write in [[wikipedia::Smalltalk|Smalltalk]]! [[Smalltalk]] is unique/strange, but I like [[Smalltalk]]'s [[Hotswap]]. Long time ago [[Smalltalk]] could do things [[Java]] is still [[Hotswap|dreaming about]]. |
== Extending Root Hierarchy Class == | == Extending Root Hierarchy Class == | ||
| - | The [[Smalltalk]] systems (as far as I remember) start with a bunch of predefined classes which everyone can modify. | + | The [[Smalltalk]] systems (as far as I remember) start with a bunch of predefined classes which everyone can use and modify. Of course, the nature of [[OOP]] system suggests to be extensible. Thus one can create new subclasses (OK, that is the same as in [[Java]]), but one can also add new methods to existing classes. Sure, lovers of meta-programming may be happy with that, but on and on, this is not a system that could work in a distributed programmning processes. |
The classical [[Smalltalk]] style to find out what is a type of an object is based on a bunch of '''isSomething''' methods: | The classical [[Smalltalk]] style to find out what is a type of an object is based on a bunch of '''isSomething''' methods: | ||
Revision as of 00:06, 15 July 2011
Dissatisfied with relational or OOP mappings of the real world? Let's create a better world inside a computer! Let's write in Smalltalk! Smalltalk is unique/strange, but I like Smalltalk's Hotswap. Long time ago Smalltalk could do things Java is still dreaming about.
Extending Root Hierarchy Class
The Smalltalk systems (as far as I remember) start with a bunch of predefined classes which everyone can use and modify. Of course, the nature of OOP system suggests to be extensible. Thus one can create new subclasses (OK, that is the same as in Java), but one can also add new methods to existing classes. Sure, lovers of meta-programming may be happy with that, but on and on, this is not a system that could work in a distributed programmning processes.
The classical Smalltalk style to find out what is a type of an object is based on a bunch of isSomething methods:
> 1 isNumber true > 'text' isNumber false > 'text' isString true
What people do when they define new types like Person? They what to have their own isPerson method. Thus they add this method to Object to return false and override it in Person class to return true:
> Object subclass: #Person > !Object methodsFor: 'Checking Person'! isPerson ^false !! > !Person methodsFor: 'Checking Person'! isPerson ^true !!
One can then easily check on any object if it is a person or not:
> 1 isPerson false > Person new isPerson true
As a result, if you want to understand a Smalltalk program, you should look at the added isSomething methods in the Object. This kind of programming creates not object oriented systems, but different flavors (in the above case a person oriented system), where capabilities of each object are driven by the variety of subclasses.
I don't like that each Smalltalk system ends up being completely unique. This is not how APIs should be designed, as that prevents merge of systems developed independently, as far as I can tell.
Is Java an OOP system?
But enough about Smalltalk and let's look at Java's root class Object. Can you guess what kind of oriented system Java is?
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