Traits

[Jonathan M Davis]

On Saturday, October 12, 2013 09:32:09 luminousone wrote:
> And again, the casting solution is a bloody hack, it is loaded
> with corner cases that will break things if you are not aware of
> them. It also requires an allocated instance of that object

Of course, it requires an instance of the object. The point is to test whether 
an instance is of a type derived from a particular type, not whether a 
particular type is derived from a particular type. If the OP wants to test 
whether a particular type is derived from another type, then casting is not 
the right solution. The way to do that is to use an is expression, e.g. 
is(Derived : Base). If you really care that the type is a derived type and 
want to avoid any other type of implicit conversions, then you need to use 
some compile time reflection to do that, but that's often overkill and 
completely kills the ability to create class which "inherits" via alias this, 
which is the main purpose for alias this existing in the first place.

> It is bad practice.

It's standard practice. Both the online docs and TDPL will tell you to use a 
cast to determine whether a particular object's type is derived from a 
particular type. And I completely disagree that it's bad practice, but clearly 
we're not going to agree on that.

- Jonathan M Davis