Abstract type: Difference between revisions

=={{header|Genyris}}==

In Genyris by default there are no constructors. In effect all classes are Abstract until they are used to tag an object.

There is no constructor for this class. To prevent the class ever being associated with an instance it suffices to force the validator to fail.

def !valid?(object) nil

 

tag Stack some-object ; always fails

 

However this is not much use if we want to use an abstract class to define an interface. Here is a quasi-abstract class which can be used to tag objects if they conform to the class's membership expectations. In this case it wants two methods, !enstack and !destack:

def !valid?(object)

object

tmp</lang>

Now we instantate a concrete object and validate that it conforms to the Abstract type:

 

=={{header|Haskell}}==