Question

abstract class DirectiveNode
{
    public static readonly RequirementOptions ArgumentOptions = RequirementOptions.Optional;
}

class IfNode : DirectiveNode
{
    static IfNode()
    {
        ArgumentOptions = RequirementOptions.Required; // error here
    }

I don’t understand the problem. I thought static IfNode() was a static constructor? Why the error?

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Just found this: Assigning to static readonly field of base class

Answer 1

Unlike nonstatic constructors, a subclass’s static constructor has no relationship with the parent static constructor. If you want the subclass to be able to change the ArgumentOptions value used by base class functions, consider a virtual property:

abstract class DirectiveNode
{
    public virtual RequirementOptions ArgumentOptions
    {
        get { return RequirementOptions.Optional; }
    }
}

class IfNode : DirectiveNode
{
    public override RequirementOptions ArgumentOptions
    {
        get { return RequirementOptions.Required; }
    }
}