Question

I’m currently looking into C# Generics, and I have a few questions.

1) In the following code, will the comparison of the type of T in “Test” slow down the program? In other languages this is handled on compile time, but I don’t know about C#.

2) Since sizeof apparently won’t work, I have to use System.Runtime.InteropServices.Marshal.SizeOf. Is this correct?

3) I haven’t seen code like this in C# yet, is there anything wrong about it, or is it perfectly fine what I’m doing here? In the end the method in this example would take a handful of types, and throw and exception if it can’t handle it. Some types would be handled independently, others like short/int/long would be handled together, depending on their size.

using System;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Test<int>();
            Test<long>();
            Test<string>();
            Console.ReadLine();
        }

        static void Test<T>()
        {
            Type type = typeof(T);

            if (type == typeof(int) || type == typeof(long))
            {
                Console.WriteLine("int");
                Console.WriteLine(System.Runtime.InteropServices.Marshal.SizeOf(type).ToString());
            }
            else if (type == typeof(string))
            {
                Console.WriteLine("string");
            }
        }
    }
}

Answer 1

Yes, the type comparison slows it down, not that such an operation will significantly affect anything done only once. If you’re doing this in a tight loop somewhere… consider not doing it. This is because it creates a Type object and compares those Type objects – it’s not a compile-time check.

Yes, Marshal.SizeOf is correct¹. I don’t know what C#’s sizeof does, though, because I’m a VB.NET person.

As for not seeing this type of code much in C#, that’s probably because it’s not a case that people often come across. And also, instead of doing what you’re doing, you should be offering method overloads for each type; cleaner, and the error is at compile-time, not runtime.

_{¹ You’re just printing it out, it’s correct to print it out. I don’t know what the goal of all this is, though.}