[/caption]I recently had the joy of picking up the book Design Patterns in Ruby which is a great book, made my Christmas wish list. If you have been living on the moon or are just one of those weird people that haven't heard of ruby yet, it is a dynamically typed interpreted language made famous by the web framework, Ruby on Rails.
Do you see what I just did right there? I gave you some background information, information that you more than likely don't need, you are reading my blog, you know what ruby is. Russ Olsen (author of Design Patterns in Ruby) does the same thing with duck typing. What is duck typing you ask? (again you probably didn't, you know what it is, or you are familiar with this thing called Google). Well it comes from the term, "If it walks like a duck, quacks like a duck, then its a duck" and according to the authority on all human knowledge it can be defined as the following
In computer programming with object-oriented programming languages, duck typing is a style of dynamic typing in which an object's current set of methods and properties determines the valid semantics, rather than its inheritance from a particular class or implementation of a specific interface.
One of the properties this gets you is the ability to pass any kind of variable anywhere and as long as it acts like the object the function is expecting it will work, no matter what class it is. In practice this allows for some great code reuse and as described in the book the evaporation of some class GoF design patterns. Olsen goes into a bit of depth about duck typing and the classic fear of someone coming from a strongly typed language.
So there is no compile time or static checks, what stops you from passing a database connection into a function that accepts an int or calling the give_big_fat_bonus method on a lowly worker instance instead of an executive instance, or of course the ceo instance which is a derived class of executive.
Anonymous Object Oriented Programmer
The answer is a resounding, nothing! (Dovetails nicely with my last post) Nothing stops you from doing this, go ahead see what happens. Depends on the language, in ruby you get a NoMethodError, and you get something like that in most duck typed languages.
The question then is how do people write any code that works, the answer is by not being full-on stupid. Ruby, and other duck typed languages, have taken to heart the sentiment of my post i can't stop you from being stupid (The shameless self promotion is getting a little rampant at this point). The language can't stop you from treating an int like a database connection, and really why should it. What in the hell are you doing mixing up an int and a database connection, you deserve to get punched in the face, a NoMethodError is the least of your worries.
But, accidents happen, so your db variable holding the database connection and your dv variable holding the direct value modifier amount are dangerously close on the keyboard. Are you going to just pray that you are 100% correct in your typing all the time, who do you think you are, me?! (I'll wait patiently as grammar-nazis and typoistas tear apart this post). This is why unit testing is so huge in duck typed languages, if you are using sweet delicious lisp then repl is your friend, ruby also has repl (irb) but its not nearly as integral to the development process as repl is to lisp. Your tests let you know that you aren't doing something stupid, and performs all the static and dynamic checking one could want.
So go out and give a duck typed language a shot, pretty soon you will enjoy the added speed, and you will realize that the static syntax checking is not necessary if you know what the hell you are doing.
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