C# 0 The Complete Reference

ByTwos

 and 

ByTwos

 would be invalid.

Comparing Instances of a Type Parameter

Sometimes you will want to compare two instances of a type parameter. For example, you 

might want to write a generic method called 

IsIn( )

 that returns true if some value is 

contained within an array. To accomplish this, you might first try something like this:

// This won’t work!

public static bool IsIn(T what, T[] obs) {

  foreach(T v in obs)

    if(v == what) // Error!

      return true;

  return false;

}

Unfortunately, this attempt won’t work. Because 

T

 is a generic type, the compiler has no 

way to know precisely how two objects should be compared for equality. Should a bitwise 

comparison be done? Should only certain fields be compared? Should reference equality be 

used? The compiler has no way to answer these questions.

To enable two objects of a generic type parameter to be compared, you must use the 

CompareTo( )

 method defined by one of .NET’s standard interfaces: 

IComparable

. This 

interface is implemented by all of C#’s built-in types, including