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Chapter ‎18   Unsafe code

7.1.1 Values of expressions

Most of the constructs that involve an expression ultimately require the expression to denote a value. In such cases, if the actual expression denotes a namespace, a type, a method group, or nothing, a compile-time error occurs. However, if the expression denotes a property access, an indexer access, or a variable, the value of the property, indexer, or variable is implicitly substituted:

The value of a variable is simply the value currently stored in the storage location identified by the variable. A variable must be considered definitely assigned (§‎5.3) before its value can be obtained, or otherwise a compile-time error occurs.

The value of a property access expression is obtained by invoking the get-accessor of the property. If the property has no get-accessor, a compile-time error occurs. Otherwise, a function member invocation (§‎7.4.3) is performed, and the result of the invocation becomes the value of the property access expression.

The value of an indexer access expression is obtained by invoking the get-accessor of the indexer. If the indexer has no get-accessor, a compile-time error occurs. Otherwise, a function member invocation (§‎7.4.3) is performed with the argument list associated with the indexer access expression, and the result of the invocation becomes the value of the indexer access expression.

7.2 Operators

Expressions are constructed from operands and operators. The operators of an expression indicate which operations to apply to the operands. Examples of operators include +, -, *, /, and new. Examples of operands include literals, fields, local variables, and expressions.

There are three kinds of operators:

Unary operators. The unary operators take one operand and use either prefix notation (such as –x) or postfix notation (such as x++).

Binary operators. The binary operators take two operands and all use infix notation (such as x + y).

Ternary operator. Only one ternary operator, ?:, exists; it takes three operands and uses infix notation (c? x: y).

The order of evaluation of operators in an expression is determined by the precedence and associativity of the operators (§‎7.2.1).

Operands in an expression are evaluated from left to right. For example, in F(i) + G(i++) * H(i), method F is called using the old value of i, then method G is called with the old value of i, and, finally, method H is called with the new value of i. This is separate from and unrelated to operator precedence.

Certain operators can be overloaded. Operator overloading permits user-defined operator implementations to be specified for operations where one or both of the operands are of a user-defined class or struct type (§‎7.2.2).

7.2.1 Operator precedence and associativity

When an expression contains multiple operators, the precedence of the operators controls the order in which the individual operators are evaluated. For example, the expression x + y * z is evaluated as x + (y * z) because the * operator has higher precedence than the binary + operator. The precedence of an operator is established by the definition of its associated grammar production. For example, an additive-expression consists of a sequence of multiplicative-expressions separated by + or - operators, thus giving the + and - operators lower precedence than the *, /, and % operators.

The following table summarizes all operators in order of precedence from highest to lowest:

Section

Category

Operators

Copyright Microsoft Corporation 1999-2003. All Rights Reserved.107

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