Editing Smalltalk (section)

==Classes==
This is a stock class definition:<ref>{{cite book|last1=Goldberg|first1=Adele|author-link1=Adele Goldberg (computer scientist)|last2=Robson|first2=David|title=Smalltalk-80 The Language|year=1989|publisher=Addison Wesley|isbn=0-201-13688-0|pages=39–53}}</ref>
<syntaxhighlight lang="smalltalk">
Object subclass: #MessagePublisher
    instanceVariableNames: ''
    classVariableNames: ''
    poolDictionaries: ''
    category: 'Smalltalk Examples'
</syntaxhighlight>
Often, most of this definition will be filled in by the environment. Notice that this is a message to the <code>Object</code> class to create a subclass named <code>MessagePublisher</code>. In other words: classes are [[first-class object]]s in Smalltalk which can receive messages just like any other object and can be created dynamically at execution time.

===Methods===
When an object receives a message, a method matching the message name is invoked. The following code defines a method publish, and so defines what will happen when this object receives the 'publish' message.
<syntaxhighlight lang="smalltalk">
publish
    Transcript show: 'Hello World!'
</syntaxhighlight>
The following method demonstrates receiving multiple arguments and returning a value:
<syntaxhighlight lang="smalltalk">
quadMultiply: i1 and: i2
    "This method multiplies the given numbers by each other and the result by 4."
    | mul |
    mul := i1 * i2.
    ^mul * 4
</syntaxhighlight>
The method's name is <code>#quadMultiply:and:</code>. The return value is specified with the <code>^</code> operator.

Objects are responsible for determining dynamically at runtime which method to execute in response to a message—while in many languages this may be (sometimes, or even always) determined statically at compile time.

===Instantiating classes===
The following code:
<syntaxhighlight lang="smalltalk">
MessagePublisher new
</syntaxhighlight>
creates (and returns) a new instance of the MessagePublisher class. This is typically assigned to a variable:
<syntaxhighlight lang="smalltalk">
publisher := MessagePublisher new
</syntaxhighlight>
However, it is also possible to send a message to a temporary, anonymous object:
<syntaxhighlight lang="smalltalk">
MessagePublisher new publish
</syntaxhighlight>