EricomQ9, C# - rextester

Language: Layout:

namespace Rextester
{
    using System;
        
    public class Program
    {
        public static void Main(string[] args)
        {
            TestMethod();
        }
        
 
        static void TestMethod()
        {
            // even if compiling with Roslyn the invalid checks below 
            // DO NOT trigger a compiler warning
            DateTime dt = DateTime.MaxValue;
            if (dt == null) { }
            bool isEq = dt == null;

// but trigger warning CS0472 for numeric types
            // The result of the expression is always 'false' since a value of type '<TYPENAME>' is never equal to 'null' of type '<TYPENAME>?'
            float i = 0;
            if (i == null) { }
            isEq = i == null;

// warning CS0464: Comparing with null of type 'DateTime?' always produces 'false'
            bool isGreater = dt > null;
            if (i > null) { }

// calling with a null argument gives a compile time error
            // CS1503: Argument 1: cannot convert from '<null>' to 'DateTime'
            //DateFunction(null);

// this is valid but condition never evaluates
            DateFunction(DateTime.MinValue);

// use a nullable type instead
            DateTimeFunction(null);
            DateTimeFunction(DateTime.MinValue);
            DateTimeFunction(DateTime.MaxValue);

}

static void DateFunction(DateTime time)
        {
            if (time == null) { /* do something */ }
            else
            {
                Console.WriteLine("Impossible null check for value types.");
                Console.WriteLine("Always evaluates to false.");
                Console.WriteLine("Should have triggered a compiler warning.");
            }
        }

static void DateTimeFunction(DateTime? time)
        {
            if (time == null) { /* do something */ }
            else { Console.WriteLine(time.Value); }            
        }
        
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,12 sec, absolute running time: 0,08 sec, cpu time: 0,08 sec, average memory usage: 12 Mb, average nr of threads: 3