Category:Smalltalk: Difference between revisions
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Classes themself are objects and as such instances of some Metaclass. As classes define and provide the protocol (=set of methods) for their instances, metaclasses define and provide the protocol for their instances, the corresponding class. Every class has its own metaclass and as such can implement new class-side messages. Typically, instance creation and utility code is found on the class side. Most Smalltalk dialects allow for the metaclass to specify and return the type of compiler or other tools to be used when code is to be installed. This allows for DSLs or other programming language syntax to be implemented seamlessly by defining a metaclass which returns a compiler for a non-Smalltalk. Typical examples for this are parser generators (tgen, ometa, petite parser), data representation specs (asn1, xml etc.) and languages (smallRuby, graphical languages in squeak etc.) |
Classes themself are objects and as such instances of some Metaclass. As classes define and provide the protocol (=set of methods) for their instances, metaclasses define and provide the protocol for their instances, the corresponding class. Every class has its own metaclass and as such can implement new class-side messages. Typically, instance creation and utility code is found on the class side. Most Smalltalk dialects allow for the metaclass to specify and return the type of compiler or other tools to be used when code is to be installed. This allows for DSLs or other programming language syntax to be implemented seamlessly by defining a metaclass which returns a compiler for a non-Smalltalk. Typical examples for this are parser generators (tgen, ometa, petite parser), data representation specs (asn1, xml etc.) and languages (smallRuby, graphical languages in squeak etc.) |
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Being objects, classes and metaclasses can be created dynamically, by sending a #subclass:... message to another class, or |
Being objects, classes and metaclasses can be created dynamically, by sending a #subclass:... message to another class, or by instantiating a new metaclass. |
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=== Exception Handling === |
=== Exception Handling === |
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