Allow var in method overrides

[TonyValenti]

Hi C# team:
When working with Overrides, it would be great if I could use var. This would save me a lot of manual refactoring work which changing types. var should work whenever it can be absolutely resolved with no ambiguity. If var would introduce an ambiguity in an override, then it should not be allowed in that situation.

Here is an example:

//Base class must have explicit types
public abstract class ExampleBase<TInput, TKey, TValue> {

  public abstract KeyValuePair<TKey, TValue> GetValues(TInput Input);

}

//Derived class can then use var
public class Example : ExampleBase<Person, string, string> {

  public override var GetValues(var Input) {
    var ret = KeyValuePair.Create("Name", Input.Name);
    return ret;
  }

}

[HaloFour]

The IDE already generates the signature for you so I don't see much point in avoiding having the explicit types in the signatures. I'd rather the clarity than having to navigate back to the base type to understand what it does. Not to mention, that wouldn't work with overloads.

[yaakov-h]

Why wouldn’t it work with overloads? You can’t overload methods on return type only.

[HaloFour]

This proposal is also using var for the parameters.

[yaakov-h]

oh I missed that detail, thanks

[Yoticc]

I'm against it.
But about your idea, I think override don't need even var, it anyway don't give any information about return type.
With the same logic, you can remove the modifier, leaving only keyword override:

override GetValues(NotVarTypeValue Input) {
    var ret = KeyValuePair.Create("Name", Input.Name);
    return ret;
  }

Probably devs want to leave information about method, so they don’t take this approach

[huoyaoyuan]

With covariant return, the return type of overridden method isn't necessarily the same of base method.
var also introduces overload resolution hell if two virtual methods are having the same name.