The alias this could be changed to allow conversion to the base
class one step at a time. I'm not happy with it since it'd
essentially do a big chain down to Object and it also ignores
interfaces, but it's a start:
static if(is(T == class) && !is(T == Object))
@property NotNull!(BaseClassesTuple!T[0]) _valueHelper() inout
{
assert(_value !is null); // sanity check of invariant
return assumeNotNull(cast(BaseClassesTuple!T[0]) _value);
}
else
@property inout(T) _valueHelper() inout
{
assert(_value !is null); // sanity check of invariant
return _value;
}
(Previously, it just had the second _valueHelper)
