Question

It might be basic question, but could anyone explain how does this work. Below code is just example, but in real time this scenario could occur in various places. For ex: While creating DTO for complex object like Customer which has Orders property. Does Orders (=List) need to be instantiated in the constructor of the Customer or just directly assign it to the result of query or a stored procedure.

List<string> list1 = new List<string>()
{
    "One", "Two","Three"
};

List<string> list2 = new List<string>();
list2 = list1;        
foreach (var s in list2)
  Console.WriteLine(s);

List<string> list3 = list1;
if (list3 != null) //is this the only difference
{
 foreach (var s in list3)     
     Console.WriteLine(s);     
}

I tried checking the IL code but it wasn’t self explanatory.

    IL_0031: stloc.0
    IL_0032: newobj instance void class [mscorlib]System.Collections.Generic.List`1<string>::.ctor()
    IL_0037: stloc.1
    IL_0038: ldloc.0
    IL_0039: stloc.1
    IL_003a: ldloc.0
    IL_003b: stloc.2
    IL_003c: nop
    IL_003d: ldloc.1
    IL_003e: callvirt instance valuetype [mscorlib]System.Collections.Generic.List`1/Enumerator<!0> class [mscorlib]System.Collections.Generic.List`1<string>::GetEnumerator()
    IL_0043: stloc.s CS$5$0000

I am sorry for posting a confusing example. Below is the actual
scenario

DTO:

public class CustomerBO
{
        public CustomerBO()
        {
            Orders = new List<OrderBO>(); 
        }
       List<OrderBO>() Orders { get; set;}
      //other properties of customer
}

Now in DAL layer:

objCustomer.Orders = Repository.GetAll<OrderBO>("dbo.GetOrdersList");

My question is would it be ok if I initialize Orders object in the CustomerBO constructor (or) skip it and check for null in the presentation layer.

Answer 1

list2: You first create an empty list, then you get rid of it and make list2 point to the same object as list1.

list3: It directly points to the same object as list1.