Question

public T Prop = new Ctor(Method);

private K Method(U controller, V request);

I get that it can’t access Method here, because Method is required to be static. Why is this? Prop is not static.

Update: Here’s the actual signature:

public DataSource(Func<ControllerBase, AjaxDataTable.Request, Result> dataSelector)

And this is how the method used to be:

public AjaxDataTable<SourcesViewModel.Source.Channel>.DataSource AjaxData =
    new AjaxDataTable<SourcesViewModel.Source.Channel>.DataSource(OnSelectData);

This wasn’t an issue because I didn’t need to reference this, so when I added this and it didn’t compile anymore, (the field wasn’t mine to begin with, someone else had done it like that, so don’t hate me for that). I changed it to the following:

private AjaxDataTable<SourcesViewModel.Source.Channel>.DataSource ajaxData;
public AjaxDataTable<SourcesViewModel.Source.Channel>.DataSource AjaxData
{
    get
    {
        if (ajaxData == null)
        {
            ajaxData =
                new AjaxDataTable<SourcesViewModel.Source.Channel>
                    .DataSource(OnDataSelector);
        }
        return ajaxData;
    }
}

But then the ajaxData private field would always be null, which makes the data table be instanced again every time (this is appended into a concurrent dictionary, which causes an Exception on a duplicate key). I want to know how assigning to a field that doesn’t reference this works. Does that create something that is reused across all instances of an object?

Answer 1

This is due to section 10.5.5.2 of the C# 4 spec, which includes:

A variable initializer for an instance field cannot reference the instance being created. Thus it is a compile-time error to reference this in a variable initializer […]

You’re effectively referencing this, as your code is equivalent to:

public T Prop = new Ctor(this.Method);

Now you can argue that this restriction is draconian, but that’s a different discussion. Note that you could put it into a constructor body:

public T Prop;

public Foo()
{
    Prop = new Ctor(Method);
}

(I’m assuming you wouldn’t really have a public field, and that you’d have sensible names, etc 🙂