#1,191 – Lambda Can’t Capture ref or out Parameters

Lambda expressions can make use of variables declared in a containing scope, i.e. outside of the expression itself.  They cannot, however, use variables that are defined as ref or out parameters in an outer scope.

In the example below, it’s a compile-time error to include the valOut parameter in the lambda expression.

        static void SomeMethod(int valIn, out int valOut)
        {
            int local;

            Action doCalc = () =>
            {
                local = valIn * 2;   // this is ok
                valOut = valIn * i;  // this is not--compile-time error
            };
        }

As an alternative, you can assign a value returned by the lambda to an out parameter.

        static void SomeMethod(int valIn, out int valOut)
        {
            // Ok to assign result of lambda to
            // out parameter
            Func<int> doCalc2 = () => valIn * 2;
            valOut = doCalc2();   // Allowed
        }
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About Sean
Software developer in the Twin Cities area, passionate about .NET technologies. Equally passionate about my own personal projects related to family history and preservation of family stories and photos.

2 Responses to #1,191 – Lambda Can’t Capture ref or out Parameters

  1. Pingback: Dew Drop – September 26, 2014 (#1864) | Morning Dew

  2. Phạm Tuân says:

    Reblogged this on Phạm Tuân blog.

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