Minor Correction: The original name of this post was Extending Classes at Runtime. For Ruby, that title is okay. For ObjC , that title is wrong(AFAIK).
This is an powerful feature which two languages I know implement: Ruby and ObjC. In ObjC, you define a category and all the methods in the category will be added to the class at runtime. Therefore, even if you are using closed-source libraries, if you wanted to add a method/correct a method for the existing class, you can create a category and do so. In Ruby, it is even easier to extend classes at runtime:
Here’s a Ruby example(usual GPL disclaimers apply, you can also get the code in the file labeled extending_classes.rb from the Box widget on the right):
#!/usr/bin/env ruby
class Array
def sum
total = 0
self.each {|elem| total += elem.to_i if elem.methods.include?(“to_i“)}
total
end
# doesn’t do what is
# intended if elements don’t support a proper to_s
def split
self.collect! {|el| el.to_s.split(/\B/) if el.methods.include?(“to_s“) }
end
end
if __FILE__ == $0
a = Array.new([1,2,3,4,5,6])
b = Array.new
b << “3“ << [1,2] << “Foobah“
c = Array.new(["a","b","c","d","1"])
puts “a.sum is #{a.sum}“
puts “b.sum is #{b.sum}“
puts “c.sum is #{c.sum}“
puts “a.split is #{a.split}“
puts “b.split is #{b.split}“
puts “C’s contents:“
c.each {|elem| puts elem}
end
