C# Language Specification

Binary operators

The following rules apply to binary operator declarations, where T denotes the instance type of the class or struct that contains the operator declaration:

• 
  A binary non-shift operator must take two parameters, at least one of which must have type T or T?, and can return any type.
  
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  A binary << or >> operator must take two parameters, the first of which must have type T or T? and the second of which must have type int or int?, and can return any type.
  

The signature of a binary operator consists of the operator token (+, -, *, /, %, &, |, ^, <<, >>, ==, !=, >, <, >=, or <=) and the types of the two formal parameters. The return type and the names of the formal parameters are not part of a binary operator’s signature.

Certain binary operators require pair-wise declaration. For every declaration of either operator of a pair, there must be a matching declaration of the other operator of the pair. Two operator declarations match when they have the same return type and the same type for each parameter. The following operators require pair-wise declaration:

• 
  operator == and operator !=
  
• 
  operator > and operator <
  
• 
  operator >= and operator <=
  

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