14.5.9 Postfix in- & decrement operators

post-increment-expression:
primary-expression ++
post-decrement-expression:
primary-expression --
The operand of a postfix 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 postfix 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
compile-time error occurs.
C# LANGUAGE SPECIFICATION
146
Unary operator overload resolution (?4.2.3) 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.
The run-time processing of a postfix 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 value of x is saved.
The selected operator is invoked with the saved value of x as its argument.
The value returned by the operator is stored in the location given by the
evaluation of x.
The saved value of x 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 and the returned value is saved.
The selected operator is invoked with the saved value of x as its argument.
The set accessor of x is invoked with the value returned by the operator as
its value argument.
The saved value of x becomes the result of the operation.
The ++ and -- operators also support prefix notation (?4.6.5). 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.