C# LANGUAGE SPECIFICATION

1• The right operand of the += or -= operator is evaluated, and, if required, converted to the type of the left

2operand through an implicit conversion (§13.1).

3• An event accessor of the event is invoked, with argument list consisting of the value computed in the

4previous step. If the operator was +=, the add accessor is invoked; if the operator was -=, the remove

5accessor is invoked.

6An event assignment expression does not yield a value. Thus, an event assignment expression is valid only

7in the context of a statement-expression (§15.6).

814.14 Expression

9An expression is either a conditional-expression or an assignment.

10expression:

1314.15 Constant expressions

14A constant-expression is an expression that can be fully evaluated at compile-time.

15constant-expression:

17The type of a constant expression can be one of the following: sbyte, byte, short, ushort, int, uint,

18long, ulong, char, float, double, decimal, bool, string, any enumeration type, or the null type.

19The following constructs are permitted in constant expressions:

20• Literals (including the null literal).

21• References to const members of class and struct types.

22• References to members of enumeration types.

23• Parenthesized sub-expressions, which are themselves constant expressions.

24• Cast expressions, provided the target type is one of the types listed above.

25• The predefined +, –, !, and ~ unary operators.

26• The predefined +, –, *, /, %, <<, >>, &, |, ^, &&, ||, ==, !=, <, >, <=, and >= binary operators, provided

27each operand is of a type listed above.

28• The ?: conditional operator.

29Whenever an expression is of one of the types listed above and contains only the constructs listed above, the

30expression is evaluated at compile-time. This is true even if the expression is a sub-expression of a larger

31expression that contains non-constant constructs.

32The compile-time evaluation of constant expressions uses the same rules as run-time evaluation of non-

33constant expressions, except that where run-time evaluation would have thrown an exception, compile-time

34evaluation causes a compile-time error to occur.

35Unless a constant expression is explicitly placed in an unchecked context, overflows that occur in integral-

36type arithmetic operations and conversions during the compile-time evaluation of the expression always

37cause compile-time errors (§14.5.12).

38Constant expressions occur in the contexts listed below. In these contexts, a compile-time error occurs if an

39expression cannot be fully evaluated at compile-time.

40• Constant declarations (§17.3).

41• Enumeration member declarations (§21.30).

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Chapter 14 Expressions

1• case labels of a switch statement (§15.7.2).

2• goto case statements (§15.9.3).

3• Dimension lengths in an array creation expression (§14.5.10.2) that includes an initializer.

4• Attributes (§24).

5An implicit constant expression conversion (§13.1.7) permits a constant expression of type int to be

6converted to sbyte, byte, short, ushort, uint, or ulong, provided the value of the constant expression

7is within the range of the destination type.

814.16 Boolean expressions

9A boolean-expression is an expression that yields a result of type bool.

10boolean-expression:

12The controlling conditional expression of an if-statement (§15.7.1), while-statement (§15.8.1), do-statement

13(§15.8.2), or for-statement (§15.8.3) is a boolean-expression. The controlling conditional expression of the

14?: operator (§14.12) follows the same rules as a boolean-expression, but for reasons of operator precedence

15is classified as a conditional-or-expression.

16A boolean-expression is required to be of a type that can be implicitly converted to bool or of a type that

17implements operator true. [Note: As required by §17.9.1, any type that implements operator true

18shall also implement operator false. end note] If neither requirement is satisfied, a compile-time error

19occurs.

20When a boolean expression is of a type that cannot be implicitly converted to bool but does implement

21operator true, then following evaluation of the expression, the operator true implementation

22provided by that type is invoked to produce a bool value.

23[Note: The DBBool struct type in §18.4.2 provides an example of a type that implements operator true

24and operator false. end note]

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