C# Language Specification

Prefix increment and decrement operators

pre-increment-expression:
++ unary-expression

pre-decrement-expression:
-- unary-expression

The operand of a prefix increment or decrement operation must be an expression classified as a variable, a property access, or an indexer access. The result of the operation is a value of the same type as the operand.

If the operand of a prefix increment or decrement operation is a property or indexer access, the property or indexer must have both a get and a set accessor. If this is not the case, a binding-time error occurs.

Unary operator overload resolution (§7.3.3) is applied to select a specific operator implementation. Predefined ++ and -- operators exist for the following types: sbyte, byte, short, ushort, int, uint, long, ulong, char, float, double, decimal, and any enum type. The predefined ++ operators return the value produced by adding 1 to the operand, and the predefined -- operators return the value produced by subtracting 1 from the operand. In a checked context, if the result of this addition or subtraction is outside the range of the result type and the result type is an integral type or enum type, a System.OverflowException is thrown.

The run-time processing of a prefix increment or decrement operation of the form ++x or --x consists of the following steps:

• 
  If x is classified as a variable:
  

• 
  x is evaluated to produce the variable.
  
• 
  The selected operator is invoked with the value of x as its argument.
  
• 
  The value returned by the operator is stored in the location given by the evaluation of x.
  
• 
  The value returned by the operator becomes the result of the operation.
  

• 
  If x is classified as a property or indexer access:
  

• 
  The instance expression (if x is not static) and the argument list (if x is an indexer access) associated with x are evaluated, and the results are used in the subsequent get and set accessor invocations.
  
• 
  The get accessor of x is invoked.
  
• 
  The selected operator is invoked with the value returned by the get accessor as its argument.
  
• 
  The set accessor of x is invoked with the value returned by the operator as its value argument.
  
• 
  The value returned by the operator becomes the result of the operation.
  

The ++ and -- operators also support postfix notation (§7.6.9). Typically, the result of x++ or x-- is the value of x before the operation, whereas the result of ++x or --x is the value of x after the operation. In either case, x itself has the same value after the operation.

An operator ++ or operator -- implementation can be invoked using either postfix or prefix notation. It is not possible to have separate operator implementations for the two notations.

6.