On 2013-02-20 15:37, Gor Gyolchanyan wrote:

After I tested this, immediately thought of the constructor. The
constructor of the base class is guaranteed to be called when
constructing a derived class, right? Even if the call is implicit, it
still happens and at the call site the concrete type being constructed
is known, so in theory, a template this parameter on the base class's
constructor should allow the base class to know the static type of the
object being constructed (which is immensely useful for implementing
dynamic dispatch classes).

class Base
{
     this(this This_)()
     {
         // Build a dispatch table using __traits(allMethods, This_)
     }

     void opCall(Payload_)(Payload_ payload_)
     {
         // Dynamically dispatch payload_ using the previously built
dispatch table.
     }
}

class Derived: Base
{
     // implicitly generated constructor will call the Base.this() and
implicitly give it the static type of Derived.
}

unittest
{
     Base b = new Derived;
     b(); // 100% transparent dynamic dispatch
}

Unfortunately, this is what DMD had to say about this:

C:\Users\g.gyolchanyan\Desktop\test.d(3): Error: found 'This_' when
expecting ')'
C:\Users\g.gyolchanyan\Desktop\test.d(3): Error: semicolon expected
following function declaration
C:\Users\g.gyolchanyan\Desktop\test.d(3): Error: Declaration expected,
not ')'

It looks like DMD thinks I was gonna write a postblit constructor and I
guess the functionality is already there, but can't be reached due to a
parsing error.

I haven't even thought about this use case. It would be so cool.

--
/Jacob Carlborg