How do I inherit from Dictionary?

c# inheritance collections

35,448

Solution 1

You were close, you just need to remove the type parameters from the constructors.

class Foo<TKey,TValue> : Dictionary<TKey, TValue>
{   
    Foo():base(){}
    Foo(int capacity):base(capacity){}
}

To override a method you can use the override keyword.

Solution 2

Not directly answering your question, just an advice. I would not inherit the dictionary, I would implement IDictionary<T,K> and aggregate a Dictionary. It is most probably a better solution:

class Foo<TKey,TValue> : IDictionary<TKey, TValue>
{   

    private Dictionary<TKey, TValue> myDict;

    // ...
}

Solution 3

If you just want the same type but with a different name, you can shorten it with using alias:

using Foo = System.Collections.Generic.Dictionary<string, string>;

and then

Foo f = new Foo();

35,448

Author by

Pratik Deoghare

Updated on July 12, 2022

Comments

Pratik Deoghare almost 2 years
I want all the functionality of Dictionary<TKey,TValue> but I want it as Foo<TKey,TValue>.
How should I go about doing this?
Currently I am using
```
class Foo<TKey,TValue> : Dictionary<TKey, TValue>
{   
    /*
     I'm getting all sorts of errors because I don't know how to 
     overload the constructors of the parent class.
    */
    // overloaded methods and constructors goes here.

    Foo<TKey,TValue>():base(){}
    Foo<TKey,TValue>(int capacity):base(capacity){}

}
```
What is the right way to overload constructors and methods of the parent class?

NOTE:I think I have misused the word 'overload' please correct it or suggest correction.
Jon Skeet over 14 years

Not within the constructors, no... they're already within the type, so they already "have" the type parameters.
ajithmanmu over 14 years

Nope, TKey and TValue are now defined as part of the class. You don't need to redefine them in each method.
Henk Holterman over 14 years

and make them public, usually.
Pratik Deoghare over 14 years

Sorry,I deleted the comment by accident.
Pratik Deoghare over 14 years

How can I make them all public without writing public in front of each one?
ajithmanmu over 14 years

public has to be explicitly defined in C#, without it everything defaults to private.
Pratik Deoghare over 14 years

I guess then I will have to override each and every constructor of the base class explicitly or is there any other way ?
Pratik Deoghare over 14 years

(+1) What do you recommend if I want to use just the Dictionary but with name Foo?
Stefan Steinegger over 14 years

Why would you do this? A kind of C-style typedef?
Polyfun over 14 years

Not quote everything defaults to private: class, struct and enum default to internal, whereas methods, properties and fields default to private.
The Chairman over 14 years

That's a Decorator (en.wikipedia.org/wiki/Decorator_pattern). Possible drawback: You need to implement each connection from your class to your member dictionary manually.
Stefan Steinegger over 14 years

@Mao: that's true, you need to implement each method, but you also might find it practical to have full control.
cowlinator over 8 years

What is the point of inheriting from Dictionary if none of the methods are virtual?
MarioDS about 8 years

@TheChairman FWIW, if you're using ReSharper, there's a very handy context action that delegates all IDictionary members to the myDict field (when fixing the "missing members" error). You can also press alt+ins and choose "Delegating members..." to insert them. Saves a lot of work!
Alex Fainshtein almost 2 years

This is true and will work. But unfortunately, Visual Studio does not provide good support for aliasing. Right-clicking Foo in the code and selecting "Go to Definition" will bring you to the definition of generic Dictionary<TKey, TValue>. And "Go to Declaration" seems plainly broken. Alas.