Part 18 - Duck Typing
| Definition: Duck Typing Duck typing is a humorous way of describing the type non-checking system. Initially coined by Dave Thomas in the Ruby community, its premise is that (referring to a value) "if it walks like a duck, and talks like a duck, then it is a duck". |
Even though Boo is a statically typed language, Duck Typing is a way to fake being a dynamic language. Duck typing allows variables to be recognized at runtime, instead of compile time. Though this can add a sense of simplicity, it does remove a large security barrier.
d as duck d = 5 // currently set to an integer. print d d += 10 // It can do everything an integer does. print d d = "Hi there" // sets it to a string. print d d = d.ToUpper() // It can do everything a string does. print d
5 15 Hi there HI THERE
Duck typing is very handy if you are loading from a factory or an unpredictable dynamic library.
| Recommendation Do not enable duck typing by default. It should only be used in a few situations. |
On a side note, The booish interpreter has duck typing enabled by default. This can be disabled by typing in interpreter.Ducky = false
Here is a practical example of where duck typing is useful.
import System.Threading def CreateInstance(progid): type = System.Type.GetTypeFromProgID(progid) return type() ie as duck = CreateInstance("InternetExplorer.Application") ie.Visible = true ie.Navigate2("http://www.go-mono.com/monologue/") while ie.Busy: Thread.Sleep(50ms) document = ie.Document print("${document.title} is ${document.fileSize} bytes long.")
Exercises
- Come up with another good example where duck typing is effective.
Go on to Part 19 - Using the Boo Compiler


