Overloading Operators in C# - Operator Overloading

Overview

Operators can be overloaded to provide more natural syntax for custom types. Operator overloading is most appropriately used for implementing custom structs that represent fairly primitive data types. For example, a custom numeric type is an excellent candidate for operator overloading.

Table 4-1 lists the overloadable symbolic operators.

Table 4-1. Overloadable symbolic operators

+ (unary)	- (unary)	!	~	++
--	+	-	*	/
%	&	|	^	<<
>>	==	!=	>	<
>=	<=

The following operators are also overloadable:

1. Implicit and explicit conversions (with theimplicitandexplicitkeywords)

2. The literalstrueandfalse

The following operators are indirectly overloaded:

1. The compound assignment operators (e.g.,+=,/=) are implicitly overridden by overriding the noncompound operators (e.g.,+,=).

2. The conditional operators&&and||are implicitly overridden by overriding the bitwise operators&and|.

Operator Functions

An operator is overloaded by declaring an operator function. An operator function has the following rules:

1. The name of the function is specified with theoperatorkeyword followed by an operator symbol.
   

2. The operator function must be markedstatic.

3. The parameters of the operator function represent the operands.

4. The return type of an operator function represents the result of an expression.

5. At least one of the operands must be the type in which the operator function is declared.

In the following example, we define a struct calledNoterepresenting a musical note, and then overload the+operator:

  public struct Note
  {
    int value;
    public Note (int semitonesFromA) { value = semitonesFromA; }

    public static Note operator + (Note x, int semitones)
    {
       return new Note (x.value + semitones);
    }
  }

This overload allows us to add anintto aNote:

  Note B = new Note(2);
  Note CSharp = B + 2;

Overloading an assignment operator automatically supports the corresponding compound assignment operator. In our example, since we overrode+, we can use+=too:

  CSharp += 2;

Next: Overloading Equality and Comparison Operators >>
 

More C# Articles
More By O'Reilly Media