Allow throw expressions in a property's initial value

[Richiban]

A bit of an unusual one, I think there could be value in allowing the following syntax for properties:

public class C
{
    public string Val { get; set; } = throw new Exception("Val has not been set");
}

The idea is that getting this property will throw an exception if its setter was never called, roughly equivalent to the following hand-written code:

public class C
{
    private bool Val_setter_called = false;
    private string Val_backing_field = null;

    public string Val 
    {
        get 
        {
            if (!Val_setter_called)
                throw new Exception("Val has not been set");
                
            return Val_backing_field;
        }
        set
        {
            Val_setter_called = true;
            Val_backing_field = value;
        }
    }
}

This is partly inspired by Powershell, where a similar syntax is allowed on function arguments:

function Foo($val = $(throw "Val was not provided"))
   ...

This would be useful anywhere a type is expected to be deserialized (and therefore something like the required keyword is of no help); a particular use case I deal with frequently is when working in dotnet applications where configuration is bound to an object, and it's extremely verbose to ensure that values are properly set without making the properties nullable and pushing the problem onto every other type that depends on one of these values.

I understand this suggestion might be controversial, but I still thought it was worth putting out there.

[HaloFour]

Feels like something a source generator and a partial property could do pretty easily?

[Richiban]

Ahh, yes! At first I thought a source generator wouldn't be able to do this because they can't wrap existing members, but I forgot partial properties were a thing. Carry on!

[jaredpar]

If you consider this the answer can you mark it as such and resolve the discussion?