Q:

Is this clean coding? (.Net, C#)

In one of our projects I found this code
class A 
{
     private B b = new B();

     protected void AMethod()
     {
         var x = b.DomeSome();
     }
}

My question, is this a "clean" way of coding? Would it be cleaner to instantiate b in AMethod?
Does is depend?

A:

If you create an instance of b in AMethod, then the variable will lost after AMethod ends. So each call of AMethod will create a new object B.
On the other hand, having the variable declared at class level (like in your example) will allow you to reuse the instance of B for all the calls of AMethod.
There is not precise answer on how is cleaner unless your provide us with more context

