![](\"http:\/\/localhost:8001\/wp-content\/uploads\/2018\/10\/drivable_class_diagram.png\")
<\/a><\/div>\nHowever, in languages like ruby, interfaces are defined implicitly, which means that two classes implement the same interface as soon as they respond to the same interface. Take a look at our example as implemented in ruby:<\/p>\n
class<\/span> Car<\/span><\/span>
public<\/span> void<\/span> drive<\/span>(<\/span>meters<\/span>)<\/span><\/span>
# start the engine<\/span><\/span>
# go for it<\/span><\/span>
end<\/span><\/span>
<\/span>
def<\/span> stop<\/span><\/span>
# stop the engine<\/span><\/span>
end<\/span><\/span>
end<\/span><\/span>
<\/span>
class<\/span> Bagger<\/span><\/span>
def<\/span> drive<\/span>(<\/span>meters<\/span>)<\/span><\/span>
# start engine<\/span><\/span>
# start left track<\/span><\/span>
# start right track<\/span><\/span>
end<\/span><\/span>
<\/span>
def<\/span> stop<\/span><\/span>
# stop left track<\/span><\/span>
# stop right track<\/span><\/span>
end<\/span><\/span>
end<\/span><\/span>
<\/span>
class<\/span> AutomatedDriver<\/span><\/span>
def<\/span> forward<\/span>(<\/span>vehicle<\/span>,<\/span> meters<\/span>)<\/span><\/span>
vehicle<\/span>.<\/span>drive<\/span>();<\/span><\/span>
vehicle<\/span>.<\/span>stop<\/span>();<\/span><\/span>
end<\/span><\/span>
end<\/span><\/span><\/code><\/pre>\nThe classes Car and Bagger still both implement the Drivable interface. But as in ruby you use the so-called ducktyping, they both implement it implicitly by just responding to the same API, consisting of drive and stop. However, even in duck-typed languages, you might want to define and document your interfaces in a central point to make sure once you change it, all implementing classes do as well. You can do this by implementing unit tests to ensure the interface is fulfilled.<\/p>\n
Following is an example of a rspec test to ensure our Drivable interface is implemented correctly.<\/p>\n
<\/p>\n
shared_examples<\/span> \"a Drivable\"<\/span> do<\/span><\/span>
it<\/span> {<\/span> expect<\/span>(<\/span>subject<\/span>).<\/span>to<\/span> respond_to<\/span>(<\/span>:drive<\/span>).<\/span>with<\/span>(<\/span>1<\/span>).<\/span>argument<\/span> }<\/span><\/span>
it<\/span> {<\/span> expect<\/span>(<\/span>subject<\/span>).<\/span>to<\/span> respond_to<\/span>(<\/span>:stop<\/span>).<\/span>with<\/span>.<\/span>