Reference Types

Aug 26, 2008
by David Cumps

Part of my 2008 study notes for exam 70-536 (.NET Framework 2.0).

Overview

Data is stored on the heap; a pointer to that data is stored on the stack.
The heap gets cleaned by the garbage collector, removing objects that are no longer referenced.
Copying reference types will only copy the pointer, not duplicate the data.
- This means altering a reference type through one variable will also be reflected when accessing it through another variable, pointing at the same heap location.
Reference types can be immutable, System.String being the best-known one.

Good practice

Use String.Concat, String.Join, String.Format or a StringBuilder when working extensively with strings.
- See String Concatenation vs Memory Allocation for a detailed analysis of string operations.

Examples

Value types vs reference types

// ---------------------------------------------------------------------------------------------
// Example of reference types.
// ---------------------------------------------------------------------------------------------
 
MyNumber a, b;
a = new MyNumber(5); // Store 5 in a
b = a;               // Copy the reference to 'MyNumber' a into b
a.X = 10;            // Modify a, but since b is pointing to the same object, b will change too
 
Console.WriteLine(a.X); // Will print 10
Console.WriteLine(b.X); // Will print 10

class MyNumber
{
    private int _x;
 
    public int X
    {
        get { return this._x; }
        set { this._x = value; }
    }
 
    public MyNumber(int x)
    {
        this._x = x;
    }
}

Strings

string[] words = new string[] { "Word1", "Word2", "Word3" };
Console.WriteLine(String.Join(" | ", words)); // Word1 | Word2 | Word3
Console.WriteLine(String.Concat(words));      // Word1Word2Word3
 
StringBuilder longString = new StringBuilder();
longString.Append("Hello World");
Console.WriteLine(longString.ToString());