How Can I Prevent Lambda Expressions from Capturing References in C#?

Preventing Reference Capture in C# Lambda Expressions

C# lambda expressions, by default, capture variables by reference. This means the lambda expression maintains a pointer to the original variable, and any changes to that variable after the lambda's creation will be reflected when the lambda is executed.

Here's an example illustrating this behavior:

class Program
{
    delegate void Action();

    static void Main(string[] args)
    {
        List<Action> actions = new List<Action>();

        for (int i = 0; i < 10; i++)
            actions.Add(() => Console.WriteLine(i));

        foreach (Action a in actions)
            a();
    }
}

Executing this code will print "10" ten times. This happens because each lambda captures a reference to the single i variable, whose value is 10 by the time the loop finishes.

To avoid this reference capture and ensure each lambda gets its own copy of the loop variable's value, create a local copy within the loop:

for (int i = 0; i < 10; i++)
{
    int copy = i; // Create a local copy
    actions.Add(() => Console.WriteLine(copy));
}

Now, each lambda captures a distinct copy variable, preserving the value at the time of its creation. The output will correctly display numbers 0 through 9.

It's crucial to understand that unlike some other languages (like C ), C# doesn't offer a direct mechanism to explicitly specify reference or value capture within the lambda expression syntax itself. Creating a local copy is the standard workaround to achieve value-capture semantics.

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