115. Statements

6Console.WriteLine("reachable");

7}

8the second invocation of Console.WriteLine is unreachable because there is no possibility that the

9statement will be executed. end example]

10A warning is reported if the compiler determines that a statement is unreachable. It is specifically not an

11error for a statement to be unreachable.

12[Note: To determine whether a particular statement or end point is reachable, the compiler performs flow

13analysis according to the reachability rules defined for each statement. The flow analysis takes into account

14the values of constant expressions (§14.15) that control the behavior of statements, but the possible values of

15non-constant expressions are not considered. In other words, for purposes of control flow analysis, a non-

16constant expression of a given type is considered to have any possible value of that type.

17In the example

18void F() {

20if (i == 2) Console.WriteLine("unreachable");

21}

22the boolean expression of the if statement is a constant expression because both operands of the

23== operator are constants. As the constant expression is evaluated at compile-time, producing the value

24false, the Console.WriteLine invocation is considered unreachable. However, if i is changed to be a

25local variable

26void F() {

28if (i == 2) Console.WriteLine("reachable");

29}

30the Console.WriteLine invocation is considered reachable, even though, in reality, it will never be

31executed. end note]

32The block of a function member is always considered reachable. By successively evaluating the reachability

33rules of each statement in a block, the reachability of any given statement can be determined.

34[Example: In the following code

35void F(int x) {

36 Console.WriteLine("start");

37if (x < 0) Console.WriteLine("negative");

38}

39the reachability of the second Console.WriteLine is determined as follows:

40• The first Console.WriteLine expression statement is reachable because the block of the F method is

41reachable (§15.2).

42• The end point of the first Console.WriteLine expression statement is reachable because that

43statement is reachable (§15.6 and §15.2).

44• The if statement is reachable because the end point of the first Console.WriteLine expression

45statement is reachable (§15.6 and §15.2).

46• The second Console.WriteLine expression statement is reachable because the boolean expression of

47the if statement does not have the constant value false.

48end example]

49There are two situations in which it is a compile-time error for the end point of a statement to be reachable:

216