Is copying performed when capturing a value-type into a lambda?

Question

struct SomeStruct
{
    public int Num { get; set; }
}

class Program
{
    static Action action;

    static void Foo()
    {
        SomeStruct someStruct = new So         


        

Answer 1

There will be no copies. Lambdas capture variables, not values.

You can use Reflector to look at the compile code: the compiler will move the "someStruct" variable into a helper class.

private static void Foo()
{
    DisplayClass locals = new DisplayClass();
    locals.someStruct = new SomeStruct { Num = 5 };
    action = new Action(locals.b__1);
}
private sealed class DisplayClass
{
    // Fields
    public SomeStruct someStruct;

    // Methods
    public void b__1()
    {
        Console.WriteLine(this.someStruct.Num);
    }
}

Copying structures will never cause user-defined code to run, so you cannot really check it that way. Actually, the code will do a copy when assigning to the "someStruct" variable. It would do that even for local variables without any lambdas.