C#7: Underscore ( _ ) & Star ( * ) in Out variable

Question

I was reading about new out variable features in C#7 here. I have two questions:

1. It says

   We allow \"discards\" as out parameters as w

Answer 1

In C# 7.0 (Visual Studio 2017 around March 2017), discards are supported in assignments in the following contexts:

• Tuple and object deconstruction.
• Pattern matching with is and switch.
• Calls to methods with out parameters.
• A standalone _ when no _ is in scope.

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Other useful notes

• discards can reduce memory allocations. Because they make the intent of your code clear, they enhance its readability and maintainability
• Note that _ is also a valid identifier. When used outside of a supported context

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Simple example : here we do not want to use the 1st and 2nd params and only need the 3rd param

(_, _, area) = city.GetCityInformation(cityName);

Advanced example in switch case which used also modern switch case pattern matching (source)

switch (exception)                {
case ExceptionCustom exceptionCustom:       
        //do something unique
        //...
    break;
case OperationCanceledException _:
    //do something else here and we can also cast it 
    //...
    break;
default:
    logger?.Error(exception.Message, exception);
    //..
    break;

}