Risk of using iterative variables in Lambda expressions

Lambda expressions provide a concise way to define inline functions in a loop. However, using iterative variables directly in lambdas may lead to unexpected behavior later.

Lambda Trap for Iterating Variables:

Consider the following code:

for (int i = 0; i  Console.WriteLine(i);
    actions.Add(action);
}

foreach (var action in actions) {
    action();
}

People might think that each lambda will print the corresponding value of i. However, all lambdas share the same capture reference to i due to closures.

Accidental print result:

When the loop exits, i becomes 10, and all lambdas now point to this final value. As a result, executing the lambda will print "10" ten times instead of the expected sequence from 0 to 9.

This behavior stems from the lambda closure maintains references to variables declared within its scope, even if the loop has been completed.

Avoidance and Alternative Methods:

To solve this problem, create a local variable in the loop and assign it to the value of the iterative variable:

for (int i = 0; i  Console.WriteLine(j);
    actions.Add(action);
}

foreach (var action in actions) {
    action();
}

This ensures that each lambda captures a different value of j, resulting in the expected print sequence.

Remember that using iterative variables directly in lambda expressions can lead to unexpected situations related to closures. Instead, consider creating local variables to accurately capture the required values.