Using 'Default' keyword on an instance of type 'Object'

Question

When supplied with an integer (or other value type) boxed as a object, I'm pretty sure there is no way to use default() (returns the default value of a given type) on it directly to return the underlying boxed default value, is this correct?

I'd rather make a call on object in a single operation without having to write a load of conditionals as follows:

public object GetDefaultVal(object obj){
 if(obj is Guid){
  return default(Guid);
 }
 if(obj is double){
  return default(double);
 }
....
}

It's very unclear what you're asking, given that your sample won't compile due to not providing a method name, and using `Default` instead of `default`. — Jon Skeet, Oct 27 '16 at 08:36
@Henningsson Doesn't typeof() return an instance of `Type`, which is therefore always going to be null... — maxp, Oct 27 '16 at 08:37
Could you make the method generic instead? Or do you really need to be able to pass a boxed integer and retrieve a boxed 0 instead, for example? — Jon Skeet, Oct 27 '16 at 08:38
@JonSkeet unfortunately not, I'm actually trying to implement `IValueConverter` — maxp, Oct 27 '16 at 08:38
You should define a generic method and than just invoke them on any object type — Megha, Oct 27 '16 at 08:39
Will this help you: http://stackoverflow.com/a/353073/580053 — Dennis, Oct 27 '16 at 08:39

score 2 · Answer 1 · answered Oct 27 '16 at 08:40

Assuming you can't change the method to be generic, you can just use the fact that all value types provide a parameterless constructor, so you can call Activator.CreateInstance:

public object GetDefaultValue(object obj)
{
    Type type = obj.GetType();
    return type.IsValueType ? Activator.CreateInstance(type) : null;
}

(The default value for all reference types is null.)

Using 'Default' keyword on an instance of type 'Object'

1 Answers1