Local Type Inference

            1. What does local type inference mean?

            2. Advantages of using local type inference?

            3. What are the cases when the var keyword is not allowed?

            The C# compiler is able to determinate a variable type inferring it from the assignment expression.

1. Better performance. Using local type inference we can avoid boxing/unboxing.

 

2. Type safety. When we use local type inference the C# compiler is able to check type in the compile time.

 

Example 1:

        static void Main(string[] args)

        {

            var x = args;

            Trace.WriteLine(x.GetType());

 

            var y = default(string);

            y = "";

            Trace.WriteLine(y.GetType());

 

            var a = 1;

            Trace.WriteLine(a.GetType());

 

            var b = 1.1;

            Trace.WriteLine(b.GetType());

 

            var c = a / b;

            Trace.WriteLine(c.GetType());

 

            var d = "string";

            Trace.WriteLine(d.GetType());

        }

 

Output:

System.String[]

System.String

System.Int32

System.Double

System.Double

System.String

 

Example 2:

    class Program

    {

        //The contextual keyword ‘var’ may only appear within a local variable declaration

        var x = 0;

 

        //The contextual keyword ‘var’ may only appear within a local variable declaration

        public static var ReturnVar() { return 0; }

 

        //The contextual keyword ‘var’ may only appear within a local variable declaration

        public static void ReturnVar(var param) { }

 

        static void Main(string[] args)

        {

            //Implicitly-typed local variables must be initialized

            var x;

 

            //Cannot assign <null> to an implicitly-typed local variable

            var t = null;

        }

    }