C# object initializer wanting to use wrong Add method
c#, dictionary, inheritance, object-initializers, polymorphism
Solution
A collection initializer does not necessarily look at any ICollection.Add(x) method. More specifically, for a collection initializer
new SpecificRow {
{ ? }
}
C# looks at any Add method with signature Add(?); if ? contains comma's, C# looks at an Add method with multiple arguments. The compiler does not have any special handling of KeyValuePair<,> at all. The reason `{ string, string }` works, is because your base class has an overload `Add(string, string)`, and not because it has an overload for `Add(KeyValuePair<string, string>)`.
So to support your syntax for
new SpecificRow {
{ MyEnum.Value, "" }
};
you need an overload of the form
void Add(MyEnum key, string value)
That's all there is to it.
Problem
I have the following class hierarchy: ``` public class Row : ICloneable, IComparable, IEquatable<Row>, IStringIndexable, IDictionary<string, string>, ICollection<KeyValuePair<string, string>>, IEnumerable<KeyValuePair<string, string>>, System.Collections.IEnumerable { } public class SpecificRow : Row, IXmlSerializable, System.Collections.IEnumerable { public void Add(KeyValuePair<MyEnum, string> item) { } } ``` However, trying to do the following gives an error: ``` var result = new SpecificRow { {MyEnum.Value, ""}, {MyEnum.OtherValue, ""} }; ``` I get this error: The best overloaded Add method 'Row.Add(string, string)' for the collection initializer has some invalid arguments How can I make it so that using an object initializer on the derived class `SpecificRow` allows type `MyEnum`? It seems like it should see the `Add` method in `SpecificRow`. Update: I implemented an extra interface on `SpecificRow` so it now looks like this: ``` public class SpecificRow : Row, IXmlSerializable, System.Collections.IEnumerable, ICollection<KeyValuePair<MyEnum, string>> { } ``` However, I still get the same `Add` error. I'm going to try implementing `IDictionary<MyEnum, string>` next.