Updating a Struct property inside a Class

Question

I know that a Struct is a value type and a Class is reference type, however I cannot seem to get around this issue.

I have a class that has a list of a struct:

public class Basket
{
  string ID{get; set;}
  List<Fruit> fruits{get;set;}

  public struct Fruit
  {
      string Name{get;set;}
      bool IsFresh;
  }
}

when passing a class instance to another class I want to update one of the Structs' IsFresh property but the code just skips it:

public class Customer
{
    public string Name{get;set;}
    public Basket Basket{get;set;}

    public Customer(string name, Basket basket)
    {
         this.Name = name;
         this.Basket = basket;
    }

    public ChangeBasket()
    {
        //CODE THAT IS NOT WORKING
        Basket.Fruits[0].IsFresh = false;
    }
}

The same referenced class is being modified and the valued structs should be updated.

why is that not working?

your property is "Basket", not "basket". does that fix it? – attila Apr 20 '14 at 14:55 — attila, Apr 20 '14 at 14:55
You can't do that. Make `Fruit` to class instead. – Sriram Sakthivel Apr 20 '14 at 15:02 — Sriram Sakthivel, Apr 20 '14 at 15:02

score 3 · Accepted Answer · edited May 23 '17 at 12:28

3

You should not generally write mutable structs. Instead, assign a whole new struct. See here. Basically what's happening is that you're modifying a copy of your struct, as it is a value type.

edited May 23 '17 at 12:28

Community

1
1

answered Apr 20 '14 at 15:04

Jordi Vermeulen

1,168
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According to the word on the street (meaning, the web) it seems that you have a point there. – Bergkamp Apr 20 '14 at 15:09

score 2 · Answer 2 · answered Apr 20 '14 at 15:18

First of all, you have some problems with access modifiers(use public when you want to access your code outside your class\structs).

Your problem is due to the reason that structs are value types, so when you access a list element you will access a copy of the element which has been returned by the indexer's "getter" of the list and not the list itself. That means if you try to update the instance, the update will not really influence a change on the "real" entity, but on the copied one and that's why you get a compilation error.

score 0 · Answer 3 · answered Apr 20 '14 at 14:57

0

This basket.Fruits[0].IsFresh = false;

should be:

Basket.fruits[0].IsFresh = false;

Does that fix it?

answered Apr 20 '14 at 14:57

Amit Joki

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Nope, that may be a typo but not the ultimate problem :( – Sriram Sakthivel Apr 20 '14 at 15:01
No, I just whipped this code for the question. the issue remains a problem – Bergkamp Apr 20 '14 at 15:02

score -1 · Answer 4 · answered Apr 20 '14 at 15:06

-1

It seems you can't use the indexer when the list is a list of structs. the following code works:

var x = Basket.Fruits[0];

x.IsFresh = false;

answered Apr 20 '14 at 15:06

TamerM

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I disagree. it doesn't. – Bergkamp Apr 20 '14 at 15:07
Actually my solution is not what you want. since its a value type, you'd be updated a whole new object instead of the original. the weird thing is that you're not getting a compile error (according to your original post). try cleaning and rebuilding – TamerM Apr 20 '14 at 15:16

Updating a Struct property inside a Class

4 Answers4