CODEWITHSUNDEEP
c#
Ally
Ally

Reputation: 4942

Variable declaration, does it create a reference to the actual object or a copy?

I'm looking at the source of a web application and I can see loads of use cases like my sample code below. I can't find any info online about when declaring a local variable in C# (of a complex type) and just want to be sure if it creates a reference or a copy of that object. Coming from a JavaScript background I'd imagine it always creates a reference unless it's a primitive data type.

The code is like this

CustomItemType myVarA = (CustomItemType) this.Session["VAR_1"];

// Do some work on the properties of VAR_1
int num2 = checked (myVarA.Items.Count - 1);
int index = 0;
while (index <= num2)
{
    myVarA.Items[index].StatusCode = "Posted";
    checked { ++index; }
}

// Save back to the session
this.Session["VAR_1"] = (object) myVarA;

Am I right in thinking that the following line isn't needed.

// Save back to the session
this.Session["VAR_1"] = (object) myVarA;

As the local variable myVarA is just a reference to the property in the session so if you update the local var then you'll also be updating the session object?

Secondly, could this pose a problem when each web page is served in a new thread that these multiple threads will be accessing the same session object and doing manipulations at the same time?

Upvotes: 3

Views: 99

Answers (1)

cyberj0g
cyberj0g

Reputation: 3787

  1. Primitive data types and structures (declared as struct) are 'by value', clasess (declared as class) are 'by reference'. So it depends on what CustomItemType is.
  2. Yes, it pose potential threads synchronization issue. In a simple case you can put object manipulations inside lock block.

Upvotes: 2

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