Re: Good idea or gimmick: Go-style OO-programming in C++ ?

From:

jeti789@web.de

Newsgroups:

comp.lang.c++

Date:

Thu, 28 Feb 2013 07:27:34 -0800 (PST)

Message-ID:

<732aa196-8ee2-49ee-a16a-7315109932bc@googlegroups.com>

But why interface may not contain checks that it is correctly used and im=

plemented? I constantly use exactly such interfaces:

  class Interface

  {

  public:

      /// doc describing what interface does for outside world

      RetType AMethod( Param param )

      {

          if ( param.isBad() )

             throw std::invalid_argument( "Interface::AMethod passed"

                                     " argument 'param' should not be bad=

..");

          if ( !isPreparedForAMethod() )

             return RetType();

          RetType ret( doAMethod( param ) );

          if ( ret.isTrash() )

             throw std::logic_error( "Interface::AMethod the implementati=

on"

" returned trash that it should not.=

");

          return ret;

      };

  private:

      /// doc describing what implementer should implement here

      virtual bool isPreparedForAMethod() const = 0;

      virtual RetType doAMethod( Param param ) = 0;

  };

Ok, you say it is *not* interface but why should I care? For me it is exa=

ctly

the *correct* way to implement an interface. It keeps concerns of interfa=

semantics and its implementation separated.

This looks to me at first sight like you were using multiple inheritance to=
do programming with traits, see http://www.codecommit.com/blog/scala/scala=
-for-java-refugees-part-5

Nothing bad about it. But you can't do that in Java since Java interfaces c=
ontain definitions only. In JDK8 methods in interfaces may define a body: h=
ttp://www.javabeat.net/2012/05/virtual-extension-methods-in-java-8/ But the=
y may still not define inst vars as traits in Scala (aka stateful traits) o=
r when using MI as in C++.

-- Oliver