Linq extension method and referencing object?

[TMattC]

Is there a good looking way of receiving an object reference instead of a new object with the linq extension methods? Id like the two code lines below to update the object within the salesLst.

// List salesLst
ProdTotalSales ps = salesLst.First(p => p.Month == o.OrderDatum.Month);
ps.Antal += r.BestSaldo;

[OriginalGriff]

It does! :laugh:

public class ProdTotalSales
{
public string Text { get; set; }
public int Value { get; set; }
public ProdTotalSales(string s, int i)
{
Text = s;
Value = i;
}
public override string ToString()
{
return string.Format("{0}:{1}", Value, Text);
}
}

ProdTotalSales p1 = new ProdTotalSales("P1", 1);
ProdTotalSales p2 = new ProdTotalSales("P2", 2);
List list = new List() { p1, p2 };
Console.WriteLine("Before:");
foreach (ProdTotalSales p in list) Console.WriteLine(p);
ProdTotalSales pn = list.First(p => p.Value == 2);
pn.Text = "P2 Modified";
Console.WriteLine("After:");
foreach (ProdTotalSales p in list) Console.WriteLine(p);

Before:
1:P1
2:P2
After:
1:P1
2:P2 Modified

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[TMattC]

Well, I made the classic mistake of attaching too little code to my question, sorry about that. The thing is that my ProdTotalSales was declared as a struct. That meant that when I was debugging, the debugger showed ps.Antal=1 but salesLst[0].Antal=0 after executing the two rows of code above. I still dont understand how that could be. Now when I changed the ProdTotalSales into being a class, it works just fine. I would really appreciate an explanation to this. Could it have something to do with me calling the default-constructor? The ProdTotalSales looked like this:

public struct ProdTotalSales
{
    public int Year { get; set; }
    public int Month { get; set; }
    public int Antal { get; set; }

    public ProdTotalSales(int \_year, int \_month, int \_antal) : this()
    {
        Year = \_year;
        Month = \_month;
        Antal = \_antal;
    }
}

[OriginalGriff]

Ah! As you say, too little code! :laugh: The thing is that a struct is always a Value type, and a class a Reference type - which means that when you assign a struct instance to another variable you ***always*** get a copy, not a reference to the existing one - and it doesn't matter if you do it directly:

        ProdTotalSales pn = list\[0\]

Or via a Linq method:

        ProdTotalSales pn = list.First(p => p.Value == 2);

You always get a copy of the data, not a reference to the original item. I wrote an article on the difference last year: Using struct and class - what's that all about?[^] which may help.

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[Simon_Whale]

after looking at this MSDN: Struct[^] is shows that struct is a value type hence how it behaves different to a class in this situation. way around your issue I am not sure at the moment.

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[TMattC]

Yes, should have thought of that. I know the struct is a value typ, though didnt think of the implications of it. Thanks for the explanation, and Ill take a peek at your article.

[OriginalGriff]

TMattC wrote:

didnt think of the implications of it.

You never do until it bites you! :laugh:

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