What's the theoretically fastest access to member of nullable type in C#?

Question

I have a field of a nullable type with a value other than null . Which of the methods below is the fastest, in theory:

1. Null conditional member access

   ThisCantBeNull?.SomeMember

2. Cast to non-nullable

   ((MyType)ThisCantBeNull).SomeMember

3. Use of the Value member of nullable types

   ThisCantBeNull.Value.SomeMember

Note that this is only a theoretical question, such minor differences do not matter, I'm only interested in how the language works and what goes on in the background.

Answer 1

Since you've already checked for null elsewhere, just get the Value , your third option.

The other two options include an extra check.

But, as noted in the comments, the performance improvement is probably minimal.

Answer 2

Just for curiosity:

public struct MyType
{
    public int SomeMember { get; set; }
}

Some very raw tests, disabling compiler optimizations :

MyType? thisCantBeNull = new MyType();
MyType someDefaultValue = new MyType();

var t1 = new Action(() => { var r = (thisCantBeNull ?? someDefaultValue).SomeMember; });
var t2 = new Action(() => { var r = ((MyType)thisCantBeNull).SomeMember; });
var t3 = new Action(() => { var r = thisCantBeNull.Value.SomeMember; });
var t4 = new Action(() => { var r = thisCantBeNull.GetValueOrDefault().SomeMember; });

const int times = 1000 * 1000 * 1000;

var r1 = t1.RunNTimes(times);
// Elapsed Timespan = 00:00:14.45115

var r2 = t2.RunNTimes(times);
// Elapsed Timespan = 00:00:07.9415388

var r3 = t3.RunNTimes(times);
// Elapsed Timespan = 00:00:08.0096765

var r4 = t4.RunNTimes(times);
// Elapsed Timespan = 00:00:07.4732878

The same tests, enabling compiler optimizations :

var r1 = t1.RunNTimes(times);
// Elapsed Timespan = 00:00:02.9142143

var r2 = t2.RunNTimes(times);
// Elapsed Timespan = 00:00:02.4417182

var r3 = t3.RunNTimes(times);
// Elapsed Timespan = 00:00:02.6278304

var r4 = t4.RunNTimes(times);
// Elapsed Timespan = 00:00:02.1725020

Where RunNTimes is:

public static TimeSpan RunNTimes(this Action a, int nTimes = 1)
{
    if (nTimes == 0)
        throw new ArgumentException("0 times not allowed", nameof(nTimes));

    var stopwatch = new Stopwatch();

    stopwatch.Start();
    for (int i = 0; i < nTimes; ++i)
        a();
    stopwatch.Stop();

    return stopwatch.Elapsed;;
}