Reference type

13y1.5kVisual Basic .NET

Data type string is a reference type. Therefore it will not create any copy in program, changes alter the result. In the following program o/p expected was:

X
Copy X
Copy A

But o/p was:

X
Copy X
Copy X

using System;

class Program
{
static void Main()
{
string s = "X";

string copy = s;
Console.WriteLine(s);
Console.WriteLine("Copy " + copy);

s = "A"; //Now "s" has been changed

Console.WriteLine("Copy " + copy);

Console.ReadKey();
}
}
/*
X
Copy X
Copy X
*/

7 Replies

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13y ago
Thank you for your explanation.
0
Vulpes13y ago
To illustrate the basic difference between reference types and value types, you need to change something so you can see whether it's the same instance or a copy.

Unfortunately, all the structs I can think of in the .NET framework are immutable - they can't be changed - and so too is the String class.

So, in my example, I thought I'd create a simple 'mutable' class and struct to illustrate the difference.
0
13y ago
So class and struct should be there and object should be instantiated in order to demonstrate difference in behavior between value type and reference type. Only along with a client program (program with Main() method) it is not possible to demonstrate difference.
0
Vulpes13y ago
OK try this example:

using System;

class C
{
public int I;

public C(int i)
{
I = i;
}
}

struct S
{
public int I;

public S(int i)
{
I = i;
}
}

class Program
{
static void Main()
{
C c = new C(3);
C d = c;
d.I = 4;
Console.WriteLine("c.I = {0}", c.I); // 4
S s = new S(3);
S t = s;
t.I = 4;
Console.WriteLine("s.I = {0}", s.I); // still 3
Console.ReadKey();
}
}

The difference between a reference type and a value type is that:

1. A variable of a reference type contains a reference (or pointer) to where an instance of that type is stored on the heap.

2. A variable of a value type contains an actual instance of the value type, not a pointer to it.

So, the variables, 'c' and 'd', both refer to the same instance of C. When C's field, I, is changed to 4 via 'd', it also changes c.I because it's the same instance.

In contrast, 't' contains a copy of the S instance contained in 's'. When S's field, I, is changed to 4 using 't', it doesn't change s.I because it's a different instance.
0
Imtiyaz13y ago
crap example!!
0
13y ago
Please support with a single program to demonstrate difference behavior between value type and reference type.
0
Vulpes13y ago
As a result of this line:

string copy = s;

the variable 'copy' now refers to the same string instance as the variable 's', namely "X".

As a result of this line:

s = "A";

the variable 's' now refers to the string instance "A".

This doesn't affect what 'copy' refers to - namely "X".

So this line:

Console.WriteLine("Copy " + copy);

prints out:

Copy X
0