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2010-05-26T15:31:53Z

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2010-05-26T12:14:45Z

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==A more practical demonstration of a base class constraint==

<source lang="csharp">using System;

class NotFoundException : ApplicationException {}

class UserID {
string name;
string number;

public UserID(string n, string num) {
name = n;
number = num;
}

public string Number {
get { return number; }
set { number = value; }
}

public string Name {
get { return name; }
set { name = value; }
}
}

class Employee : UserID {
public Employee(string n, string num) : base(n, num)
{
}
}

class Manager : UserID {
public Manager(string n, string num) :
base(n, num) { }
}

class Guest {
}

class IDList<T> where T : UserID {
T[] userIDList;
int end;

public IDList() {
userIDList = new T[10];
end = 0;
}

public bool add(T newEntry) {
if(end == 10) return false;

userIDList[end] = newEntry;
end++;

return true;
}

public T findByName(string name) {
for(int i=0; i<end; i++) {
if(userIDList[i].Name == name)
return userIDList[i];

}
throw new NotFoundException();
}

public T findByNumber(string number) {

for(int i=0; i<end; i++) {
if(userIDList[i].Number == number)
return userIDList[i];
}
throw new NotFoundException();
}
}

class MainClass {
public static void Main() {
IDList<Employee> plist = new IDList<Employee>();
plist.add(new Employee("T", "1"));
plist.add(new Employee("G", "6"));
plist.add(new Employee("M", "5"));

try {
Employee frnd = plist.findByName("T");
Console.Write(frnd.Name + ": " + frnd.Number);
} catch(NotFoundException) {
Console.WriteLine("Not Found");
}

Console.WriteLine();

IDList<Manager> plist2 = new IDList<Manager>();
plist2.add(new Manager("G", "8"));
plist2.add(new Manager("C", "9"));
plist2.add(new Manager("N", "2"));

try {
Manager sp = plist2.findByNumber("8");
Console.WriteLine(sp.Name + ": " + sp.Number);
} catch(NotFoundException) {
Console.WriteLine("Not Found");
}
}
}</source>
<pre class=codeResult>T: 1
G: 8</pre>

==A simple demonstration of a base class constraint.==

<p>Because of the base class constraint, all type arguments passed to Test must have A as a base class.</p>

<source lang="csharp">using System;

class A {
public void hello() {
Console.WriteLine("Hello");
}
}

class B : A { }

class C { }

class Test<T> where T : A {
T obj;

public Test(T o) {
obj = o;
}

public void sayHello() {
obj.hello();
}
}

class MainClass {
public static void Main() {
A a = new A();
B b = new B();
C c = new C();

Test<A> t1 = new Test<A>(a);

t1.sayHello();

Test<B> t2 = new Test<B>(b);

t2.sayHello();

// The following is invalid because
// C does not inherit A.
// Test<C> t3 = new Test<C>(c); // Error!
}
}</source>
<pre class=codeResult>Hello
Hello</pre>

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в 15:31, 26 мая 2010

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