Programming in C# Comparison (Sorting) CSE 494R (proposed course for 459 Programming in C#) Prof. Roger Crawfis

Comparison Comparing two instances of a type has many of the same properties and pitfalls as testing for equality. Equality is generally more fussy. Only two protocols for a type providing its own comparison: The IComparable interface The > and < operators

IComparable The IComparable<T> and IComparable interfaces allow for sorting or ordering of a collection. They are used in the Array.Sort method. public interface IComparable <T>{ int CompareTo(T other); // -1 if this < other, 0 if this == other, 1 if this > other } 5.CompareTo(7) => -1 “World”.CompareTo(“Hello”) => 1 32.CompareTo(8*4) => 0

IComparable Classes implementing IComparable are Values types like Int32, Double, DateTime, … The class Enum as base class of all enumeration types The class String Defines a type to be is-a IComparable.

The > and < operators Value types that have a clear context independent concept of less than and greater than should implement the < and > operators. These are compiled statically into the code, making value types more efficient.

Programming in C# Comparison (Sorting) CSE 494R (proposed course for 459 Programming in C#) Prof. Roger Crawfis