Value Types and Reference Types

Value Types and Reference Types.cs

using System;

/* Differences between Value Types and Reference Types
 *
 * Value Types:
 *      All numeric data types
 *      Boolean, Char, and Date
 *      All Structures, even if the members of the struct are reference types
 *      Enumerations, since their underlying type is always SByte, Short, Integer, Long, Byte, UShort, UInteger, or ULong
 *      
 * Reference Types:
 *      Strings
 *      All arrays, even if their elements are value types
 *      Class types
 *      Delegates
 *      
 * When a value-type instance is created, a single space in memory is allocated to store the value. When the runtime deals with a value type
 * it's dealing directory with its underlying data
 * 
 * When a reference-type instance is created, and object is created in memory, and handled through a separate reference (much like a pointer)
 * 
 */


class FractionClass //reference type
{
    public int numerator;
    public int denominator;
}

public struct FractionStruct //value type
{
    public int numerator;
    public int denominator;
}

public class Program
{
    static void RefType()
    {
        FractionClass fc1 = new FractionClass // the reference object fc1 (on the stack) is referencing the Fraction object on the heap 
        {
            numerator = 1,
            denominator = 2
        };
        FractionClass fc2 = fc1; // fc2 only copies a reference to fc1, which will point to the object on the heap

        fc2.numerator = 100; // this changes the value on the heap, so any references to fc2 (or fc1) will refer to the same value on the heap
        Console.WriteLine(fc1.numerator);
    }

    static void ValueType()
    {
        FractionStruct fs1 = new FractionStruct // fs1 and it's values placed directly on the stack. there is nothing on the heap
        {
            numerator = 2,
            denominator = 4
        };
        FractionStruct fs2 = fs1; // fs2 is now a copy of fs1 (including all it's members) 
                                  // fs2 becomes it's own object that carries it's own values. still nothing on the stack.
        fs2.numerator = 200;      // fs2 is it's own object and contains it's own members. it has no reference to fs1. fs1 and fs2 are seperate objects with seperate members
        Console.WriteLine(fs2.numerator);

    }

    public static void Main()
    {
        Console.Write("FractionClass numerator: ");
        RefType();

        Console.Write("FractionStruct numerator: ");
        ValueType();

        Console.ReadKey();
    }
}