C# Language Specification

Anonymous functions

For a lambda-expression or anonymous-method-expression expr with a body (either block or expression) body:

• 
  The definite assignment state of an outer variable v before body is the same as the state of v before expr. That is, definite assignment state of outer variables is inherited from the context of the anonymous function.
  
• 
  The definite assignment state of an outer variable v after expr is the same as the state of v before expr.
  

The example

delegate bool Filter(int i);

void F() {
int max;

// Error, max is not definitely assigned

Filter f = (int n) => n < max;

max = 5;
DoWork(f);

}

generates a compile-time error since max is not definitely assigned where the anonymous function is declared. The example

delegate void D();

void F() {

int n;
D d = () => { n = 1; };

d();

// Error, n is not definitely assigned
Console.WriteLine(n);
}

also generates a compile-time error since the assignment to n in the anonymous function has no affect on the definite assignment state of n outside the anonymous function.

4.