Virtual static member

[Ralfeus]

Hi all.
I have a base class and several classes inherited from this base
class. I need to create a instances counter for each class. I thought
about something like creation of virtual static member in the base
class and increasing it in each derived class constructor. But it's
not possible to create a virtual data member. Which alternative way
can be? Or only way is to create a static data member in each class?
Thank you

 

[Jon Skeet [C# MVP]]

I have a base class and several classes inherited from this base
class. I need to create a instances counter for each class. I thought
about something like creation of virtual static member in the base
class and increasing it in each derived class constructor. But it's
not possible to create a virtual data member. Which alternative way
can be? Or only way is to create a static data member in each class?

You either need a static variable in each class, or a base static
variable which is a Dictionary<Type,int> which keeps a count for each
type. Then in the base class constructor just do (with appropriate
locking):

int count;
counter.TryGetValue(GetType(), out count);
count++;
counter[GetType()] = count;

Jon

 

[Ralfeus]

Oh, that's exactly what I need
Thank you very much

I have a base class and several classes inherited from this base
class. I need to create a instances counter for each class. I thought
about something like creation of virtual static member in the base
class and increasing it in each derived class constructor. But it's
not possible to create a virtual data member. Which alternative way
can be? Or only way is to create a static data member in each class?

You either need a static variable in each class, or a base static
variable which is a Dictionary<Type,int> which keeps a count for each
type. Then in the base class constructor just do (with appropriate
locking):

int count;
counter.TryGetValue(GetType(), out count);
count++;
counter[GetType()] = count;

Jon

 

[Guest]

I'm sure you wouldn't do the GetType() twice. ;-)

 

[Peter Duniho]

I'm sure you wouldn't do the GetType() twice. ;-)

Why not?

I think there's a chance that the compiler can optimize that anyway
(assuming the method resolves to some simple inspection of the data
structure...I don't really know how it works though), but even if it
doesn't the code is simpler without caching the value. Why bother caching
it before you even know there's a problem calling the method twice?

 

[Guest]

Why not?

I think there's a chance that the compiler can optimize that anyway
(assuming the method resolves to some simple inspection of the data
structure...I don't really know how it works though), but even if it
doesn't the code is simpler without caching the value. Why bother caching
it before you even know there's a problem calling the method twice?

I would not assume that there is a problem occuring only for this multiple
call, but I would personaly see it as bad style.
But that's maybe a metter of taste and not programming skill.

All the best,

Martin