Part 18 - Duck Typing
| Info |
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| title | Definition: Duck Typing |
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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.
| Code Block |
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| borderStyle | solid |
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| title | Duck Typing Example |
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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
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| No Format |
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| bgColor | #D8DDE9 |
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| borderStyle | solid |
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| title | Output |
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5
15
Hi there
HI THERE
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Duck typing is very handy if you are loading from a factory or an unpredictable dynamic library.
| Tip |
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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.
| Code Block |
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| borderStyle | solid |
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| title | Practical Duck Typing |
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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.")
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Exercises
- Come up with another good example where duck typing is effective.
Go on to Part 19 - Using the Boo Compiler
