I am not an expert on this, but here is what I've found.
Considering the line:
if (typeof(IAuditableEntity).IsAssignableFrom(entity.GetType()))
versus
if (entity is IAuditableEntity)
I set up a test project, created an IAuditableEntity interface, a
class that implements it, and issues the 2 different "if" statements.
Then I opened the assembly with reflector, to see the MSIL code that
is generated.
Using "entity is IAuditableEntity" results in:
L_008b: ldloc.1 // loads local var at index 1 ("entity")
onto the evaluation stack
L_008c: isinst is_test.IAuditableEntity // pops the top
var off the evaluation stack, testing if it's an instance of
IAuditableEntity
Using "typeof(IAuditableEntity).IsAssignableFrom(entity.GetType())
results in:
L_00b3: ldtoken is_test.IAuditableEntity // Converts a
metadata token to its runtime representation, pushing it onto the
evaluation stack
L_00b8: call class [mscorlib]System.Type [mscorlib]
System.Type::GetTypeFromHandle(valuetype [mscorlib]
System.RuntimeTypeHandle) // Gets the type of IAuditableEntity
from the handle we just pushed onto the stack
L_00bd: ldloc.1 // pushes "entity" onto the stack (local
var at index 1)
L_00be: callvirt instance class [mscorlib]System.Type [mscorlib]
System.Object::GetType()
L_00c3: callvirt instance bool [mscorlib]
System.Type::IsAssignableFrom(class [mscorlib]System.Type)
So using the "is" operator issues a single IL instruction: isint.
Using if (typeof(IAuditableEntity).IsAssignableFrom(entity.GetType()))
results in:
+ ldtoken instruction
+ function call (System.Type::GetTypeFromHandle)
+ virtual call (System.Object::GetType())
+ virtual call (System.Type::IsAssignableFrom)
Keep in mind that virtual calls are more expensive than regular
function calls as well.
I would use the "is" operator. It's a built in operator that issues a
single IL instruction.
On Dec 18, 3:09 pm, "Stefan Sedich" <[email protected]> wrote:
> Heh what a post to wake upto, thanks guys, I will look into using the
> events look 100 times easier.
>
> Cheers
> Stefan
>
>
>
> On Fri, Dec 19, 2008 at 7:00 AM, Will Shaver <[email protected]> wrote:
> > Now you've just got me all confused and showing my ignorance. ;)
>
> > On Thu, Dec 18, 2008 at 1:55 PM, Tuna Toksöz <[email protected]> wrote:
>
> >> and assuming you are not talking about managed c++
>
> >> On Thu, Dec 18, 2008 at 11:52 PM, Tuna Toksöz <[email protected]> wrote:
>
> >>> boxing in c++?
> >>> Are you sure that casting takes cycles? I think it doesn't, because it is
> >>> the cmpilers job to cast.
>
> >>> On Thu, Dec 18, 2008 at 11:25 PM, Will Shaver <[email protected]>
> >>> wrote:
>
> >>>> Yes, but with both Daniel and Tuna's examples are incomplete.
> >>>> if (typeof(IAuditableEntity).IsAssignableFrom(entity.GetType())) {
> >>>> ((IAuditableEntity) entity).Audit();
> >>>> }
> >>>> or
> >>>> if (entity is IAuditableEntity) {
> >>>> ((IAuditableEntity) entity).Audit();
> >>>> }
> >>>> In BOTH cases you have to do TWO casts. In mine you only have to do one.
> >>>> I learned in C++ where casting and boxing take cycles.
> >>>> -Will
>
> >>>> On Thu, Dec 18, 2008 at 1:17 PM, Tuna Toksöz <[email protected]> wrote:
>
> >>>>> or
>
> >>>>> if (entity is IAuditableEntity)
> >>>>> ? :)
>
> >>>>> On Thu, Dec 18, 2008 at 11:08 PM, Daniel Fernandes
> >>>>> <[email protected]> wrote:
>
> >>>>>> Beside the point I know but :
> >>>>>> if (typeof(IAuditableEntity).IsAssignableFrom(entity.GetType())) {
> >>>>>> to
> >>>>>> var auditable = entity as IAuditableEntity;
> >>>>>> if (auditable != null) {
>
> >>>>>> isn't easier to read ?
>
> >>>>>> On Dec 18, 6:35 am, "Stefan Sedich" <[email protected]> wrote:
> >>>>>> > Hello,
>
> >>>>>> > I am setting date last modified audit on an entity, I implement an
> >>>>>> > IAuditableEntity interface and use a helper to set the date
> >>>>>> > modified:
>
> >>>>>> > public override bool OnFlushDirty(object entity, object id,
> >>>>>> > object[]
> >>>>>> > currentState, object[] previousState, string[] propertyNames,
> >>>>>> > global::NHibernate.Type.IType[] types) {
>
> >>>>>> > if
> >>>>>> > (typeof(IAuditableEntity).IsAssignableFrom(entity.GetType())) {
>
> >>>>>> > // If entity is auditable as this is only an update
> >>>>>> > set the last modified date.
> >>>>>> > SetValue(propertyNames, currentState, item =>
> >>>>>> > item.LastModified, DateTime.Now);
>
> >>>>>> > }
>
> >>>>>> > return false;
> >>>>>> > }
>
> >>>>>> > Type safe helper:
>
> >>>>>> > public void SetValue<T>(string[] propertyNames, object[] state,
> >>>>>> > Expression<System.Func<IAuditableEntity, T>> propertyExpression, T
> >>>>>> > value) {
>
> >>>>>> > var memberExpression = propertyExpression.Body as
> >>>>>> > MemberExpression;
> >>>>>> > if (memberExpression == null)
> >>>>>> > throw new ArgumentException("The member expression
> >>>>>> > was
> >>>>>> > not a valid member expression.");
>
> >>>>>> > string name = memberExpression.Member.Name;
> >>>>>> > int index = propertyNames.ToList().IndexOf(name);
>
> >>>>>> > if(index == -1)
> >>>>>> > throw new
> >>>>>> > InvalidOperationException(string.Format("Property {0} does no exist
> >>>>>> > on
> >>>>>> > entity.", name));
>
> >>>>>> > state[index] = value;
>
> >>>>>> > }
>
> >>>>>> > Now the question is, I saw that you must set the current state and
> >>>>>> > not
> >>>>>> > the entity directly why would
>
> >>>>>> > var ent = entity as IAuditableEntity;
> >>>>>> > ent.LastModified = DateTime.Now;
>
> >>>>>> > Not work properly or will it be fine to do this?
>
> >>>>>> > Thanks
>
> >>>>>> > --
> >>>>>> > Stefan Sedich
> >>>>>> > Software Developerhttp://weblogs.asp.net/stefansedich
>
> >>>>> --
> >>>>> Tuna Toksöz
> >>>>>http://tunatoksoz.com
>
> >>>>> Typos included to enhance the readers attention!
>
> >>> --
> >>> Tuna Toksöz
> >>>http://tunatoksoz.com
>
> >>> Typos included to enhance the readers attention!
>
> >> --
> >> Tuna Toksöz
> >>http://tunatoksoz.com
>
> >> Typos included to enhance the readers attention!
>
> --
> Stefan Sedich
> Software Developerhttp://weblogs.asp.net/stefansedich
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