Nullable Extension Methods an Non-Null Values

[TonyValenti]

Hi C# Team,
I think that I use be able to use nullable extension methods on non-null values. for example:

public static class DateTimeExtensions {
  public static boo Test(this DateTime? Value){
    return true;
  }
}

...

DateTime.Now.Test();  // <- This should work because DateTime converts to a DateTime?.

[MkazemAkhgary]

Simply write non nullable overload.

If you write extension for double, you can not use int as instance argument. Even though int is implicitly assignable to double. Same story for Foo and FooBase. Same story here.

[Logerfo]

Consider the following code:

public static class DateTimeExtensions {
  public static bool Test(this DateTime? Value){
    return true;
  }
  public static bool Test(this DateTime Value){
    return true;
  }
}

...

DateTime.Now.Test();

Today, that's valid. If your proposal gets implemented, the code does not compile anymore, since the overload resolution will result in an ambiguous match. That would be a breaking change.

[TonyValenti]

Actually if my proposal were to get implemented, I would expect normal overload resolution rules to apply and for the most specific overload to be selected.

On Mon, Dec 18, 2017 at 5:31 AM Logerfo ***@***.***> wrote: Consider the following code: public static class DateTimeExtensions { public static bool Test(this DateTime? Value){ return true; } public static bool Test(this DateTime Value){ return true; } } ... DateTime.Now.Test(); Today, that's valid. If your proposal gets implemented, the code does not compile anymore. It would be a breaking change. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <https://github.com/dotnet/csharplang/issues/1193#issuecomment-352400636>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AM-qVodSU86HtJNNvuXaBdUKhcMhybzGks5tBkz3gaJpZM4REZso> .

-- Tony Valenti