Reference Types
Part of my 2008 study notes for exam 70-536 (.NET Framework 2.0).
Overview
- Data stored on the heap, a pointer to that data is stored on the stack.
- The heap gets cleaned by the garbage collector, removing items which don’t have a reference to it anymore.
- 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 most known one.
Good practice
- Use String.Concat, String.Join, String.Format or a StringBuilder when excessively working with strings.
- See String Concatenation vs Memory Allocation for 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());
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