Re: duct typing and interface in C++

From:
James Kanze <james.kanze@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Sat, 30 Jul 2011 11:51:46 -0700 (PDT)
Message-ID:
<08bc7d5d-8ed3-4353-824a-bff5184d5c34@d32g2000yqa.googlegroups.com>
On Jul 24, 7:23 pm, TP <Tribulati...@Paralleles.invalid> wrote:

Alain Ketterlin wrote:

class Daffy : public InterfaceDuck
Inheritance must be explicit for the types to be compatible.


In fact, I would like to have duck typing exactly as in
Python: in Python there is no need to have an inheritance
relation between the interface and the class Daffy. In my
previous post, I pointed to an example with no such
inheritance relation:

http://stackoverflow.com/questions/289176/how-is-duck-typing-differen...
the-old-variant-type-and-or-interfaces

I would like to have a construction where the following
affectation is possible:

InterfaceDuck * d = new Daffy;

without inheritance relation between InterfaceDuck and Daffy.
The fact that Daffy has a method Quack() as InterfaceDuck
should be enough to allow that.

But perhaps there is no means to do that in C++?


There isn't. Python and C++ are designed to fulfill different
roles. Duck typing would make C++ inappropriate for many of the
roles it now fills. Duck typing means, for example, only
finding out about errors at runtime. No big deal in a small
program, written in a language without a compiler, in an
interactive development environment, and where robustness isn't
paramount. Not having duck typing means having to go back and
add the proper base classes every time you extend a class to
support a new protocol. Not appropriate in an experimental and
highly dynamic environment, and overkill (and a lot of extra
work) in very small, frequently changing programs.

--
James Kanze

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