getting this Type

Question

class TestClass
{
    public void Test()
    {
        //which is faster?
        object o1 = MethodRequiringType(typeof(TestClass));
        object o2 = MethodRequiringType(this.GetType());
        //which is better?
        //does it matter?
    }

    public object MethodRequiringType(Type t)
    {
        return new { }; 
    }
}

and now that I'm searching... http://stackoverflow.com/questions/983030/type-checking-typeof-gettype-or-is http://stackoverflow.com/questions/139607/what-is-the-difference-between-mycustomer-gettype-and-typeofcustomer-in-c — froadie, Jul 09 '10 at 19:08
Your two statements are not always equivalent. So the answer to the questions for which one is "better" or whether it "matters" is: it depends. — Esteban Araya, Jul 09 '10 at 19:11
@Esteban - You're absolutely right. I suppose the better question is "when should you use which?". — Seattle Leonard, Jul 09 '10 at 19:38

score 3 · Answer 1 · answered Jul 09 '10 at 19:03

3

Worry about correctness before performance. If there are any classes derived from TestClass, you won't get the same result.

answered Jul 09 '10 at 19:03

Ben Voigt

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What if it was a sealed class? – Seattle Leonard Jul 09 '10 at 19:08
Then you'd get the same `Type`, and `typeof` will get it faster. – Ben Voigt Jul 09 '10 at 21:23

Swift · Accepted Answer · 2010-07-09T21:43:53.147

3

A quick google search revealed this:

GetType is a call that is made at runtime on an instance of an object. typeof() is resolved to a call at runtime, but loads the type from the token for the type. They probably resolve to the same call, it's just that GetType requires an instance. If I didn't need the instance, I would use typeof.

and also:

Also be aware that GetType is virtual, and gives you the type of the object, not the declared type of the reference. That is:

Object o = new String();

typeof(o) Object type

o.GetType() String type

edited Jul 09 '10 at 21:43

answered Jul 09 '10 at 19:06

Swift

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In your second example, didn't you mean `o.GetType()` instead of `typeof(o)` ? – Ben Voigt Jul 09 '10 at 21:24

score 2 · Answer 3 · answered Jul 09 '10 at 19:08

2

I've actually measured this difference for a lecture I once gave (on reflection and optimization).

Bottom line: if you plan on calling that line several billion times, you'll save a second using the typeOf() instead of the GetType()

answered Jul 09 '10 at 19:08

SWeko

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I read somewhere (http://msdn.microsoft.com/en-us/magazine/cc163759.aspx) with regard to Reflection that the call to GetType was specifically optimized in the JIT compiler, since it is such a commonly used method, as opposed to other Reflection operations such as finding the MemberInfo for a specific member of a type. – Dr. Wily's Apprentice Jul 09 '10 at 19:57
`GetType` is optimized. That still doesn't make it as fast as `typeof`. – Ben Voigt Jul 10 '10 at 06:59
@Ben, I definitely agree. I didn't mean to sound like I was suggesting to use GetType over typeof in general, so thanks for catching me on that. The article actually mentions that the typeof operation is optimized as well. – Dr. Wily's Apprentice Jul 10 '10 at 20:14
What I'm saying is that the difference is not at all important. There are lots of performance bottlenecks with more impact, than saving a few nanoseconds on a GetType/typeof – SWeko Jul 10 '10 at 20:32

getting this Type

3 Answers3