Contrary to answers here, I found (object) == faster than object.ReferenceEquals. As to how faster, very negligible!
Test bed:
I know you need reference equality check, but I'm including static object.Equals(,) method as well in case of classes where its not overriden.
Platform: x86; Configuration: Release build
class Person {
}
public static void Benchmark(Action method, int iterations = 10000)
{
Stopwatch sw = new Stopwatch();
sw.Start();
for (int i = 0; i < iterations; i++)
method();
sw.Stop();
MsgBox.ShowDialog(sw.Elapsed.TotalMilliseconds.ToString());
}
Test:
Person p1 = new Person();
Person p2 = new Person();
bool b;
Benchmark(() =>
{
b = (object)p1 == (object)p2; //960 ~ 1000ms
b = object.ReferenceEquals(p1, p2); //~ 1250ms
b = object.Equals(p1, p2); //2100ms
b = EqualityComparer<Person>.Default.Equals(p1, p2); //~4000ms
}, 100000000);
Person p1 = new Person();
Person p2 = null;
bool b;
Benchmark(() =>
{
b = (object)p1 == (object)p2; //990 ~ 1000ms
b = object.ReferenceEquals(p1, p2); // 1230 ~ 1260ms
b = object.Equals(p1, p2); //1250 ~ 1300ms
b = EqualityComparer<Person>.Default.Equals(p1, p2); //~3100ms
}, 100000000);
Person p1 = null;
Person p2 = null;
bool b;
Benchmark(() =>
{
b = (object)p1 == (object)p2; //960 ~ 1000ms
b = object.ReferenceEquals(p1, p2); //1260 ~ 1270ms
b = object.Equals(p1, p2); //1180 ~ 1220ms
b = EqualityComparer<Person>.Default.Equals(p1, p2); //~3100ms
}, 100000000);
Person p1 = new Person();
Person p2 = p1;
bool b;
Benchmark(() =>
{
b = (object)p1 == (object)p2; //960 ~ 1000ms
b = object.ReferenceEquals(p1, p2); //1260 ~ 1280ms
b = object.Equals(p1, p2); //1150 ~ 1200ms
b = EqualityComparer<Person>.Default.Equals(p1, p2); //3700 ~ 3800ms
}, 100000000);
object.Equals(,) calls ReferenceEquals internally and if they are not equal it would call the overriden virtual Equals method of the class, and hence you see the notice the speed difference.
Results were consistent in Debug configuration too...
As pointed out, emphasis should be on Readability/meaningfulness/revealing intent.
