Re: [aus-dotnet] GetType or Type.GetType

[Piers Williams]

> On 10/25/05, Matt wrote:
>  
>
> > Does anyone know if is slower using Type.GetType(string) over
> > GetType(type) when using .Net types? (not user defined)
> >
> > I'm guessing there would be as the Type class would be using a lot of
> > checking but i'm just too lazy to write a test and thought some guru
> > might know.
> >    
you'd expect a fairly big difference, and there is: nearly 100x:

GetType() : 2106
object.GetType() : 2982
Type.GetType(string) : 139757

Second pass
GetType() : 1326
object.GetType() : 2895
Type.GetType(string) : 127049

[10000 iterations; ignore the units, just consider the ratios]

Bear in mind that Type.GetType(string) has got all kinds of work to do. 
Even in the simplest case  - you just specify a type name - it's pretty 
much got to scan all the in-memory structures for the current assembly 
and see if they match the type name you've provided (I guess there might 
be a name -> type handle lookup map to optimize this, but...). Worse, if 
you provide a fully qualified type name, and if the referenced 
assembly's not been loaded yet, it's going to go out to the CLR loader, 
which might start poking about in the GAC. In both cases the type name 
has to be parsed to work out what you wanted. You see where this is going.
what's interesting is the difference between using the GetType() 
function (typeof in C#) and object.GetType(). I thought they were pretty 
much the same thing, but GetType() / typeof() gets to shortcut all the 
polymorphic mucking about in object.GetType() by using an internal 
pointer directly to the type handle:
IL (same for VB / C#)

GetType() / typeof()
 IL_000d:  ldtoken    [mscorlib]System.String
 IL_0012:  call       class [mscorlib]System.Type 
[mscorlib]System.Type::GetTypeFromHandle(valuetype 
[mscorlib]System.RuntimeTypeHandle)
object.GetType()
 IL_0045:  ldsfld     string [mscorlib]System.String::Empty
 IL_004a:  callvirt   instance class [mscorlib]System.Type 
[mscorlib]System.Object::GetType()
Type.GetType(string)
 IL_007d:  ldstr      "System.String"
 IL_0082:  call       class [mscorlib]System.Type 
[mscorlib]System.Type::GetType(string)
so I guess the moral is to always use GetType() / typeof() if you've got 
the option. But you'd be doing that anyway (right?), because then you 
can't make a typo. If you're late binding for architectural (decoupling 
/ plugin) reasons then the performance hit is irrelevant anyway (it's 
not like we're talking about a 'put the kettle on' type delay)
--
piers
senior developer, UnisysWest

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