CODEWITHSUNDEEP
c#objectvalue-typereference-type
Rahul
Rahul

Reputation: 47

Avoid object instantiation in loops c# - How this can be avoided?

Here is the scenario

I know that class are reference types and Structures are value types

Below is Code1 which successfully outputs the Output1 which is expected functionality because as a new obj is created a new ref point is created and added to the persons list.

In code2. The same Object is getting assigned and as the code describes the foreach loop is actually updating the same reference that Obj is pointing all the time. At the end of for loop execution, final value is assigned to all the list items as in Output2

For case Code1 upon CAST tool review we are getting "Avoid object instantiation in loops".I know instantiation objects in for loop takes extra memory and performance too which is what I guess CAST tool is telling us. In such scenarios is there any solution that we can avoid new object instatiation inside the loop.

Using Structures is one solution based on the present scenario. But i would like to have any other ideas.

Code 1

   public class person
   {
       public string name { get; set; }
       public int age { get; set; }
   }

class Program
{
    static void Main(string[] args)
    {

        List<person> personList = new List<person>();

        for (int i = 0; i < 10; i++)
        {
        person Obj = Obj = new person();
            Obj.name = "Robert" + i;
            Obj.age = i * 10;
            personList.Add(Obj);
        }

        foreach(person indv in personList)
        {
            Console.WriteLine(indv.name + indv.age);
        }

    }
}

Output

Robert00 Robert110 Robert220 Robert330 Robert440 Robert550 Robert660 Robert770 Robert880 Robert990

Code 2

  List<person> personList = new List<person>();
        person Obj = Obj = new person();
        for (int i = 0; i < 10; i++)
        {
            Obj.name = "Robert" + i;
            Obj.age = i * 10;
            personList.Add(Obj);
        }

        foreach(person indv in personList)
        {
            Console.WriteLine(indv.name + indv.age);
        }

Output 2

Robert990 Robert990 Robert990 Robert990 Robert990 Robert990 Robert990 Robert990 Robert990

Upvotes: 1

Views: 3567

Answers (3)

jcharlesworthuk
jcharlesworthuk

Reputation: 1079

There is nothing wrong with instantiating those objects so I can't think why your tool is telling you that. At the end of the day the whole point of your code is to create a list of "person" objects. Whether you did it in a loop, or typed out all 10 instantiations in a row, it wouldn't make a difference. The loop is obviously better.

On another note though, you can really simplify this code by using linq, try writing it this way and see if your tool gives you the same warning:

List<person> personList = Enumerable.Range(1, 9).Select(x => 
new person { name = "Robert" + x, age = x * 10 }).ToList();

Upvotes: 1

maniak1982
maniak1982

Reputation: 717

I mainly avoid instantiation in loops in cases where I want to use the object outside of the loop and it isn't being added to a collection. Additionally it wouldn't be necessary if I were instantiating in the loop and passing the object to another method within the loop. In that case you can instantiate outside of the loop and pass the values to the method within the loop. If this is all of the code that you're going to use, move the Console.WriteLine inside of the loop and don't bother instantiating inside of the loop.

But I get the impression that you're trying to create a collection of objects inside a loop to be used outside of that loop. In that case, your collection of objects isn't going to have any bigger memory footprint simply because you instantiated the objects inside the loop. As you can see, if you instantiate the object outside of the loop, you're simply assigning a new value to the same object and then adding a reference to the same object multiple times to the array. You'll need to instantiate each object in the array no matter what you do.

Upvotes: 0

Yuval Itzchakov
Yuval Itzchakov

Reputation: 149588

I know instantiation objects in for loop takes extra memory and performance too which is what I guess CAST tool is telling us.

That's incorrect. An allocation will have the same "price" when used inside or outside that loop. I'm assuming your tool is warning you because allocating objects in a loop on each iteration may cause alot of objects to be instansiated, but that's exactly what's needed here. There is absolutely no need to avoid object allocation in this case.

I'd be more worried about that particular tool you're using and the advice it brings.

Upvotes: 8

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