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5.3.3.23 && expressions

Visual Studio .NET 2003

For an expression expr of the form expr-first && expr-second:

  • The definite assignment state of v before expr-first is the same as the definite assignment state of v before expr.
  • The definite assignment state of v before expr-second is definitely assigned if the state of v after expr-first is either definitely assigned or "definitely assigned after true expression". Otherwise, it is not definitely assigned.
  • The definite assignment state of v after expr is determined by:
  • If the state of v after expr-first is definitely assigned, then the state of v after expr is definitely assigned.
  • Otherwise, if the state of v after expr-second is definitely assigned, and the state of v after expr-first is "definitely assigned after false expression", then the state of v after expr is definitely assigned.
  • Otherwise, if the state of v after expr-second is definitely assigned or "definitely assigned after true expression", then the state of v after expr is "definitely assigned after true expression".
  • Otherwise, if the state of v after expr-first is "definitely assigned after false expression", and the state of v after expr-second is "definitely assigned after false expression", then the state of v after expr is "definitely assigned after false expression".
  • Otherwise, the state of v after expr is not definitely assigned.

In the example

class A
{
   static void F(int x, int y) {
      int i;
      if (x >= 0 && (i = y) >= 0) {
         // i definitely assigned
      }
      else {
         // i not definitely assigned
      }
      // i not definitely assigned
   }
}

the variable i is considered definitely assigned in one of the embedded statements of an if statement but not in the other. In the if statement in method F, the variable i is definitely assigned in the first embedded statement because execution of the expression (i = y) always precedes execution of this embedded statement. In contrast, the variable i is not definitely assigned in the second embedded statement, since x >= 0 might have tested false, resulting in the variable i being unassigned.

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