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C# LANGUAGE SPECIFICATION

constant-declarators: constant-declarator constant-declarators   ,   constant-declarator

constant-declarator: identifier   =   constant-expression

A constant-declaration may include a set of attributes (§‎17), a new modifier (§‎10.2.2), and a valid combination of the four access modifiers (§‎10.2.3). The attributes and modifiers apply to all of the members declared by the constant-declaration. Even though constants are considered static members, a constant-declaration neither requires nor allows a static modifier. It is an error for the same modifier to appear multiple times in a constant declaration.

The type of a constant-declaration specifies the type of the members introduced by the declaration. The type is followed by a list of constant-declarators, each of which introduces a new member. A constant-declarator consists of an identifier that names the member, followed by an “=” token, followed by a constant-expression (§‎7.15) that gives the value of the member.

The type specified in a constant declaration must be sbyte, byte, short, ushort, int, uint, long, ulong, char, float, double, decimal, bool, string, an enum-type, or a reference-type. Each constant-expression must yield a value of the target type or of a type that can be converted to the target type by an implicit conversion (§‎6.1).

The type of a constant must be at least as accessible as the constant itself (§‎3.5.4).

The value of a constant is obtained in an expression using a simple-name (§‎7.5.2) or a member-access (§‎7.5.4).

A constant can itself participate in a constant-expression. Thus, a constant may be used in any construct that requires a constant-expression. Examples of such constructs include case labels, goto case statements, enum member declarations, attributes, and other constant declarations.

As described in §‎7.15, a constant-expression is an expression that can be fully evaluated at compile-time. Since the only way to create a non-null value of a reference-type other than string is to apply the new operator, and since the new operator is not permitted in a constant-expression, the only possible value for constants of reference-types other than string is null.

When a symbolic name for a constant value is desired, but when the type of that value is not permitted in a constant declaration, or when the value cannot be computed at compile-time by a constant-expression, a readonly field (§‎10.4.2) may be used instead.

A constant declaration that declares multiple constants is equivalent to multiple declarations of single constants with the same attributes, modifiers, and type. For example

class A { public const double X = 1.0, Y = 2.0, Z = 3.0; }

is equivalent to

class A { public const double X = 1.0; public const double Y = 2.0; public const double Z = 3.0; }

Constants are permitted to depend on other constants within the same program as long as the dependencies are not of a circular nature. The compiler automatically arranges to evaluate the constant declarations in the appropriate order. In the example

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