| Recipe 2.8: Creating Abstract Methods |
Last Updated: Sep 8, 2003
Status: Very Likely
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Problem:
You want to declare that a given method exists, and perhaps what its signature is, but you want to leave the definition of that method to subclasses.
Solution:
Declare the method using the is abstract property:
class MyClass {
method do_something is abstract;
}
Discussion:
Abstract methods or classes in perl6 are created by using the is abstract property. It specifies that no implementation has been given; the usual intent is to provide an actual implementation later, in subclasses.
If an abstract method is actually called (that is, if the method is ever called in a situation in which the method has still received no implementation) an exception is thrown.
Note that the is abstract property is different from the yada-yada-yada operator, "...". The latter is merely a placeholder: it declares that the method will have an implementation, but that the implementation will be specified later in the code.
Note that simply neglecting to provide implementations for a method or class is a syntax error in Perl6: use either is abstract or ... as a visual cue that the method indeed has no implementation (i.e. that you really meant to do that.)
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