C#•3y ago

Modify property of object in List [Answered]

I have a struct like this:

public struct MyStruct
{
    public ulong Id { get; set; }

    public string MyProperty { get; set; }
}

public struct MyStruct
{
    public ulong Id { get; set; }

    public string MyProperty { get; set; }
}

And I have a List<MyStruct>. I want to modify MyProperty for a certain MyStruct in the list, using the Id property. I tried this:

MyList.Where(x => x.Id == id).ToList().ForEach(x => x.MyProperty = myVariable);

MyList.Where(x => x.Id == id).ToList().ForEach(x => x.MyProperty = myVariable);

But it didn't work.

5 Replies

TheBoxyBear•3y ago

MyStruct is a struct so you can't change the value of properties Loop or not Ir you need to edit the properties, make it a class to make it a reference type $ref

MODiX•3y ago

https://cdn.discordapp.com/attachments/364492811489509376/692833980650881084/pass-by-reference-vs-pass-by-value-animation.gif

mtreit•3y ago

Yes, use a class if you want mutable properties. In general structs should be immutable. Now, knowing that a struct is passed by value (meaning a copy is made when you access it), you COULD achieve what you want even using structs - by mutating the copy and then putting that copy back into the list.

List<MyStruct> data = new();

for (int i = 0; i < 10; i++)
{
    data.Add(new MyStruct { Id = (ulong)i, MyProperty = i.ToString() });
}

for (int i = 0; i < data.Count; i++)
{
    var item = data[i];
    item.MyProperty = item.MyProperty + " MODIFIED!";
    data[i] = item;
}

foreach (var item in data)
{
    Console.WriteLine(item.MyProperty);
}

List<MyStruct> data = new();

for (int i = 0; i < 10; i++)
{
    data.Add(new MyStruct { Id = (ulong)i, MyProperty = i.ToString() });
}

for (int i = 0; i < data.Count; i++)
{
    var item = data[i];
    item.MyProperty = item.MyProperty + " MODIFIED!";
    data[i] = item;
}

foreach (var item in data)
{
    Console.WriteLine(item.MyProperty);
}

However, this is doing a bunch of extra work for no good reason - just use a class instead. You could also achieve this with ref locals if the data was an array instead of a list. Again though, I would just use a class or a record.

BujjuOP•3y ago

Thanks

Accord•3y ago

✅ This post has been marked as answered!

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Modify property of object in List [Answered]