Ask HN: Is there a way to define classes at runtime in any language?

[Allocator2008]

I was just thinking about chatbots, and the ability to make logical deductions. Like Men are Mortals, Socrates is a man, so Socrates is mortal. So Mortals could be the superclass, men could be the subclass, and Socrates could be an instance of the subclass men, and would be a member of superclass Mortals. But it would be nice to have a way of defining these classes at runtime, so in a chatbot if the user posed such a scenario to the chatbot, the chatbot could use some pattern matching, construct the classes on the fly, and figure out the relations, thereby sounding "intelligent". Can this be done? Classes made at runtime instead of compile time?

[benhoyt]

In Python you can create a class at "runtime" using "type(name, bases, dict)" as per http://docs.python.org/library/functions.html#type

You can also use "new.classobj(name, bases, dict)" -- not quite sure what the difference is.

[paulgb]

You would probably want to implement your own concept of classes to do this, in which case you wouldn't have to restrict yourself to languages where classes could be declared at runtime.

But if you really wanted to use the language's classes, there are languages that support it. Javascript is one. I think Ruby lets you do this too. Python lets you declare classes at runtime, but I don't think it gives you as much flexibility as the former two. Still, any of the three should be powerful enough to do what you want. Scheme will let you do it too.

[inklesspen]

Certainly you can define classes at runtime. But I think this is the wrong way to go about logical reasoning. What happens when you want to express that Socrates is a dead Greek philosopher? Do you have DeadMortal (subclass of Mortal with isDead() returning true), GreekMortal, PhilosopherMortal (subclass of UnemployedMortal)?

I think you may get further if you look at a language like Prolog -- work along the lines of predicates, rules, and attributes.

[_pius]

See this (old) presentation for thinking along these lines:

http://www.jroller.com/obie/entry/deep_integration_of_ruby_a...

[stonemetal]

There are several languages that allow dynamic creation of classes. Any of the dynamically typed scripting languages can do that javascript, python, perl, ruby, etc.