"Common type" of the ternary operator expressions

[Ali Çehreli]

Ali Çehreli wrote:
> "Conditional Expressions" on this page covers the ternary operator as well:
> 
>   http://digitalmars.com/d/2.0/expression.html#ConditionalExpression
> 
> It says "the second and third expressions are implicitly converted to a 
> common type which becomes the result type of the conditional expression."
> 
> How "common" should the "common type" be? Wouldn't you expect the 
> following ternary operator's result be I, instead of Object?
> 
> interface I {}
> class A : I {}

My expectation is that the hierarchy of A should look like this:

Object
  |
  I
  |
  A

For me, Object should always be at the top. I know that interfaces can 
not inherit from classes; but as now the interfaces may have 
implementations, perhaps it's time to make Object an interface, as 
opposed to a class?

> class B : I {}
> 
> void foo(I) {}
> 
> void main()
> {
>     bool some_condition;
>     foo(some_condition ? new A : new B);  // <-- compiler error
> }
> 
> Compiler error:
> 
> Error: function deneme.foo (I _param_0) is not callable using argument 
> types (Object)
> Error: cannot implicitly convert expression (some_condition ? new A : 
> new B) of type object.Object to deneme.I

Thank you,
Ali