Programming style - duck type
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WHAT IS - 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. PROGRAMMING STYLE DUCK TYPING Presented by Abdun Nur Tomal
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Transcript of Programming style - duck type
WHAT IS -
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.PR
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Presented by Abdun Nur Tomal
DEFINE -
may be phrased as follows:"When I see a bird that walks like a duck and swims like a duck and quacks like a duck, I call that bird a duck.“
In duck typing, one is concerned with just those aspects of an object that are • used, • rather than with the type of the object itself.
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FOR EXAMPLE :- in a non-duck-typed language, one can create a function that takes an object of type Duck and calls that object's -walk and -quack methods.
In a duck-typed language, > the equivalent function would take an
object of any type and > call that object's walk and quack
methods. > If the object does not have the methods that
are called then the function signals a run-time error.
> It is this action of any object having the correct walk and quack methods being accepted by the function that evokes the quotation and hence the name of this form of typing.
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EXAMPLE :- Duck typing is aided by habitually not testing for the type of arguments in method and function bodies,
relying on documentation, clear code, and testing to ensure correct use.
pseudo-code for a duck typed language:
function calculate(a, b, c) => return (a+b)*c
example1 = calculate (1, 2, 3)
example2 = calculate ([1, 2, 3], [4, 5, 6], 2)
example3 = calculate ('apples ', 'and oranges, ', 3)
print to_string example1
print to_string example2
print to_string example3
the result of the code would be:9
[1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6]
apples and oranges, apples and oranges, apples and oranges
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Thus, duck typing allows polymorphism without inheritance.
The only requirement that function calculate needs in its variables is having the "+" and the "*" methods.
The duck test can be seen in the following example:As far as the function in_the_forest is concerned, the Person object is a
duck:
class Duck: def quack(self):print("Quaaaaaack!") def feathers(self): print("The duck has white and gray feathers.")
class Person: def quack(self): print("The person imitates a duck.") def feathers(self): print("The person takes a feather from the ground and shows it.") def name(self): print("John Smith") def in_the_forest(duck): duck.quack() duck.feathers()
def game(): donald = Duck() john = Person() in_the_forest(donald) in_the_forest(john)
game()
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This way software can be developed by extending partially working duck typed code.
In JavaScript
var Duck = function () {};
Duck.prototype = {
quack: function () { alert("Quaaaaaack!"); },
feathers: function () { alert("The duck has white and gray feathers."); }
};
var Person = function () {};
Person.prototype = {
quack: function () { alert("The person imitates a duck."); },
feathers: function () { alert("The person takes a feather from the ground and shows it.");},
name: function () { alert("John Smith"); }
};
var in_the_forest = function (duck)
{
duck.quack();
duck.feathers();
};
var game = function ()
{
var donald = new Duck();
var john = new Person();
in_the_forest(donald)
in_the_forest(john)
};
game();
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Resources –Wikipediahttp://en.wikipedia.org/wiki/Duck_typing#Concept_examples
Dr. Dobb’s
http://drdobbs.com/cpp/184401971
http://drdobbs.com/open-source
Big Dingus
http://bigdingus.com/2007/12/08/just-what-is-this-javascript-object-you-handed-me/
Apache Commons
http://commons.apache.org/proxy/
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Resources –Wikipediahttp://en.wikipedia.org/wiki/Duck_typing#Concept_examples
Dr. Dobb’s
http://drdobbs.com/cpp/184401971
http://drdobbs.com/open-source
Big Dingus
http://bigdingus.com/2007/12/08/just-what-is-this-javascript-object-you-handed-me/
Apache Commons
http://commons.apache.org/proxy/
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