CSharp - is operator and pattern variables

Introduction

You can introduce a variable when using the 'is' operator:

if (a is Circle s)
    Console.WriteLine (s.Radius);

This is equivalent to:

Circle s;
if (a is Circle)
{
    s = (Circle) a;
    Console.WriteLine (s.Radius);
}

The pattern variable introduced is available in the current scope, so the following is legal:

if (a is Circle s && s.Radius > 100000)
     Console.WriteLine ("Big");

And it remains in scope outside the is-expression, allowing this:

if (a is Circle s && s.Radius > 100000){
       Console.WriteLine ("Big");
}
else{
       s = new Circle();   // s is in scope
}
Console.WriteLine (s.Radius);  // Still in scope

• Previous
• Next