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OOP
Basics

Define a class

Declare a class named Greeter that takes a string on creation and greets using this string if you call the "greet" method.
python
class Greeter(object):
""" Greet someone.
"""
def __init__(self, whom):
self._whom = whom
def greet(self):
print "Hello, %s!" % self._whom

Greeter("world").greet()
clojure
(defprotocol IGreeter
(greet [this]))

(deftype Greeter [whom]
IGreeter
(greet [this]
(println (str "Hello, " whom))))

(greet (Greeter. "world"))
(defn greeter [whom]
{:whom whom})

(defn greet [g]
(println (str "Hello, " (:whom g))))

(greet (greeter "world"))
cpp
class Greeter
{
public:
Greeter(const std::string& whom);
void greet() const;

private:
std::string whom;
};

int main()
{
Greeter* gp = new Greeter("world");
gp->greet();
delete gp;
}

Greeter::Greeter(const std::string& whom) : whom(whom) {}

void Greeter::greet() const
{
std::cout << "Hello, " << whom << std::endl;
}
public ref class Greeter
{
public:
Greeter(String^ whom);
void greet();

private:
initonly String^ whom;
};

int main()
{
(gcnew Greeter(L"world"))->greet();
}

Greeter::Greeter(String^ whom) : whom(whom) {}

void Greeter::greet()
{
Console::WriteLine(L"Hello, {0}", whom);
}

Instantiate object with mutable state

Reimplement the Greeter class so that the 'whom' property or data member remains private but is mutable, and is provided with getter and setter methods. Invoke the setter to change the greetee, invoke 'greet', then use the getter in displaying the line, "I have just greeted {whom}.".

For example, if the greetee is changed to 'Tommy' using the setter, the 'greet' method would display:

Hello, Tommy!

The getter would then be used to display the line:

I have just greeted Tommy.
python

class Greeter(object):
_whom = None

def __init__(self, whom):
self._whom = whom

@property
def whom(self):
return self._whom

@propset(whom)
def whom(self, value=None):
self._whom = value

def greet(self):
print 'Helo, %s!' % self._whom

greeter = Greeter('Winston')
greeter.greet()
greeter.whom = 'Tommy'
greeter.greet()
# required for Python 2.5 or less
def propset(prop):
assert isinstance(prop, property)
def helper(func):
return property(prop.fget, func, prop.fdel, prop.__doc__)
return helper

class Greeter(object):
_whom = None

def __init__(self, whom):
self._whom = whom

@property
def whom(self):
return self._whom

@propset(whom)
def whom(self, value=None):
self._whom = value

def greet(self):
print 'Helo, %s!' % self._whom

greeter = Greeter('Winston')
greeter.greet()
greeter.whom = 'Tommy'
greeter.greet()
clojure
(defn greeter [whom]
(atom {:whom whom}))

(defn get-whom [g]
(:whom @g))

(defn set-whom [g whom]
(swap! g #(conj % {:whom whom})))

(defn greet [g]
(println (str "Hello, " (:whom @g) "!")))

; using the "class"
(let [g (greeter "world")]
(greet g)
(set-whom g "Tommy")
(greet g)
(println (str "I have just greeted " (get-whom g) ".")))

; or same effect without using any variables
(println (str "I have just greeted "
(get-whom (doto (greeter "world")
(greet)
(set-whom "Tommy")
(greet)))
"."))
cpp
#include <iostream>

using namespace std;

class Greeter {
string whom_;

public:
Greeter(const string &whom) : whom_(whom) {}

string get_whom() const {
return whom_;
}

void set_whom(const string &whom) {
whom_ = whom;
}

void greet() const {
cout << "Hello " << whom_ << "!" << endl;
}
};

int main()
{
Greeter greeter("world");
greeter.greet();
greeter.set_whom("Tommy");
greeter.greet();
cout << "I have just greeted " + greeter.get_whom() << "." << endl;
}