C# Error CS8159 – Cannot return the range variable ‘{0}’ by reference

C# Error

CS8159 – Cannot return the range variable ‘{0}’ by reference

Reason for the Error & Solution

Cannot return the range variable by reference

Example

The following sample generates CS8159:

// CS8159.cs (7,74)

using System.Linq;
class TestClass
{
    delegate ref char RefCharDelegate();
    void TestMethod()
    {
        var x = from c in "TestValue" select (RefCharDelegate)(() => ref c);
    }
}

To correct this error

To return a range variable, refactoring to return by value correct this error:

using System.Linq;
class TestClass
{
    delegate char RefCharDelegate();
    void TestMethod()
    {
        var x = from c in "TestValue" select (RefCharDelegate)(() => c);
    }
}