220 39706 <16c8ccb9-8e42-46cc-9129-52e1129617be@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: rmbeer2@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: new feature: declare data that replaces the previous one, or similar situation.... Date: Sat, 11 Aug 2018 08:50:01 -0700 (PDT) Lines: 803 Approved: news@gmane.org Message-ID: <16c8ccb9-8e42-46cc-9129-52e1129617be@isocpp.org> References: <3a9e87f5-de59-4297-8096-f8f887b9f656@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1089_674701743.1534002601469" X-Trace: blaine.gmane.org 1534002478 16778 195.159.176.226 (11 Aug 2018 15:47:58 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sat, 11 Aug 2018 15:47:58 +0000 (UTC) Cc: rmbeer2@gmail.com, cppljevans@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDI6L6W3SYLBBKULXTNQKGQEVCVVOOY@isocpp.org Sat Aug 11 17:47:53 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw1-f71.google.com ([209.85.161.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1foW7N-0004GK-HH for gclcip-std-proposals@m.gmane.org; Sat, 11 Aug 2018 17:47:53 +0200 Original-Received: by mail-yw1-f71.google.com with SMTP id t10-v6sf16795680ywc.7 for ; Sat, 11 Aug 2018 08:50:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=cwNt6/bLbryb/3mBFryV8pbt8X5S2Vp/sitKwbwfPv8=; b=CFUTkJPFWg8nzKAibDUnpDgfIwukyIUs/WoVatJPecj1vAFMsfB8PNxjZKdJlYsemM oO1+2axvDB6SdutgHr0VQbFbe9eZ5OZXW/ntmw6YSWYZee33QVIC/BBegb6BF6VpV/Uc gZWL/gOD4ls4O/y6SvGyETIu6WVqT+zNNINCxB0Sd6xPNDTnM3dpBQp97QSTNAN9Q9xP 8YVuckQgtIEr/GRA9qclD/iORrCBvt1PmeQu38Fa0Y2zcybEnrgjVJSznEdW72aPu1TW yKDK8LVnzVlwjKHdbxAsd/TFQ5zfXw3a53yqy7BL8hWFl1MeFyWgduu4nTWSi+QdxOne /yew== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=cwNt6/bLbryb/3mBFryV8pbt8X5S2Vp/sitKwbwfPv8=; b=TelIzPku3M1eTNMvI/eHVFxYBah60fGVENu3tJc2pHJ3ULsDEqZCm5Guu5UcrzloIk LDmeCCU5y6lL2hUTxpkvNEfwa8ex0iNYkw0n4w5InfgsPRx0dQOzngaxUAsWLdJyY1uf oW0n0dzriCSReYtKxLqtXVX2ZA49bx97yHFUl8twx6J3pEGR/gY1m0bV9ydgOjFbB2vc 13/7HbuZsrXLMBV2zbn9Wtb4KkaTCldnjk2p6mq3yWG2iY+cabWkFNWUPRLX3Crfte6w 9djjgynP1a7DddTKo6E88DcOpVjHz7Y+VdlNpwmr81dTFmk0/ZFUJsdGcJbZRpUkuDRb o+hQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:message-id:in-reply-to :references:subject:mime-version:x-original-sender:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=cwNt6/bLbryb/3mBFryV8pbt8X5S2Vp/sitKwbwfPv8=; b=WidWljpCKHi2IkgRd1rK3PJZjJJ+KBbUgPW4zU7nfFApW0XiGvFENRXsvmJnKInYF9 tNjlDCiClx5pZ2sgqJLcpguRjlEZ4e8n7f/X642TTewSGGqsT3aUCWo25580w+krf14V BS8VQnqDF2xWfzqM9gimUab2PVXljv9qvvCfs0ryKIs8KzbuAFrWvX/bXv/2ztUgYSev rtlvwL23AcwxAtsOEai/XWoQftzvXztjXepZlXU6hT7+YU0u8R7mzAAQIAfyh3GRmtHD l3D5HaxXyS35X7hEnly22+uQG0F3tjhdzx2PAF9x9qK3VypRmp/bJPAB/MysKWheObZ+ 1SHw== X-Gm-Message-State: AOUpUlH3TAJLXeEVAxL0Nga6itmX/Z5Kaxy0NGMBHv3zYyiDSDT0IECY npEn6Ww5sfTRv+ewPbKzKJMbRw== X-Google-Smtp-Source: AA+uWPws5+A+Pi+Jvycr76AEeRxf1/njzov0EO/ZWtv8/Wvd5nQz7F/9u41l936eOGHnNhoNKXQtHQ== X-Received: by 2002:a0d:fd46:: with SMTP id n67-v6mr3479151ywf.60.1534002603665; Sat, 11 Aug 2018 08:50:03 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a25:e68a:: with SMTP id d132-v6ls2472231ybh.9.gmail; Sat, 11 Aug 2018 08:50:02 -0700 (PDT) X-Received: by 2002:a25:8448:: with SMTP id r8-v6mr124842ybm.2.1534002602109; Sat, 11 Aug 2018 08:50:02 -0700 (PDT) In-Reply-To: <3a9e87f5-de59-4297-8096-f8f887b9f656@isocpp.org> X-Original-Sender: rmbeer2@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:39706 Archived-At: ------=_Part_1089_674701743.1534002601469 Content-Type: multipart/alternative; boundary="----=_Part_1090_899285510.1534002601470" ------=_Part_1090_899285510.1534002601470 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable La soluci=C3=B3n que me ofrecieron en este lugar fue esta: Codigo: =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D class B1 { public: virtual B2& GetB2() const =3D 0; }; class B2 {}; class D2 : public B2 {}; class D1 : public B1 { public: D1(D2& d2) : itsD2(d2) {}; virtual D2& GetB2() const {return itsD2;} private: mutable D2& itsD2; }; =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D Pero tiene el problema de que luego necesitas reemplazar todo "itsD2." por= =20 "GetB2().", esto es una mala practica y solo crea codigo basura. Al final= =20 es mejor utilizar el lenguaje C en el medio, algo asi como remplazar estas= =20 lineas por las otras siguientes: Original: GetB2().var; GetB2().var; GetB2().var; Mejorado: D2&d2=3D*((D2)itsD2); d2.var; d2.var; d2.var; Es decir, hacer una referencia de un "void*itsD2;" desde B1 en lugar de un= =20 "mutable D2&itsD2;" en D1.... la finalidad de esta propuesta es utilizar "d2.var" en lugar de=20 "GetB2().var", insisto en que mi propuesta es la mejor, si no logran=20 mejorar C++ para aceptar el uso de este tipo de variables entonces voy a=20 insistir en el viejo habito de C... El mi=C3=A9rcoles, 25 de julio de 2018, 14:16:43 (UTC-3), rmb...@gmail.com= =20 escribi=C3=B3: > > Yes, that's exactly what I was looking for! > I did not know that the keyword 'mutable' had to be used, although there= =20 > is still the problem of having to use the virtual function to directly=20 > extract the class already converted from a parent class... > The class structure that I use is similar, but directly uses a "D2=20 > itsD2;", a direct statement within the class itself... > > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D > > si, es justamente lo que estaba buscando!... > no sabia que habia que usar la palabra clave 'mutable', aunque sigue=20 > estando el problema de tener que usar la funcion virtual para extraer=20 > directamente la clase ya convertida desde una clase padre... > La estructura de clases que yo uso es similar, pero usa directamente un= =20 > "D2 itsD2;", una declaraci=C3=B3n directa dentro de la propia clase... > > El mi=C3=A9rcoles, 18 de julio de 2018, 7:04:33 (UTC-3), cpplj...@gmail.c= om=20 > escribi=C3=B3: >> >> >> >> On Monday, June 11, 2018 at 7:17:54 PM UTC-5, rmb...@gmail.com wrote: >>> >>> We have 2 classes that contain different data sets, one needs to use th= e=20 >>> functions and variables of another class, so it is included as a member= =20 >>> pointing to the other class: >>> >>> member >>> A -------> B >>> >>> Code: >>> --------------------------------------- >>> >>> class A { >>> public: >>> A(int z_) : z(z_) { } >>> int z; >>> }; >>> >>> class B { >>> public: >>> B() : a(1) { } >>> void f2() { >>> std::cout << "A:" << a.z << std::endl; >>> } >>> A a; >>> }; >>> >>> --------------------------------------- >>> >>> Then you need to create an inheritance for each class, since you need t= o=20 >>> cover a new interface layer. Let's call C and D, where C uses the base= =20 >>> class A and D uses the base class B. >>> >>> member >>> A ---------> B >>> | | >>> |inheritance | inheritance >>> | | >>> v member v >>> C ---------> D >>> >>> Code: >>> --------------------------------------- >>> >>> class A { >>> public: >>> A(int z_) : z(z_) { } >>> int z; >>> }; >>> class C: public A { >>> public: >>> C(int y_) : y(y_), A(y_) { } >>> long y; >>> }; >>> >>> class B { >>> public: >>> B() : a(1) { } >>> void f2() { >>> std::cout << "A:" << a.z << std::endl; >>> } >>> A a; >>> }; >>> class D: public B { >>> public: >>> B() : a(3) { } >>> void f2() { >>> std::cout << "A:" << a.z << std::endl; >>> } >>> C a; >>> }; >>> >>> --------------------------------------- >>> >>> Here where the problems appear, if you create B you can access the data= =20 >>> of A with the functions of B. But if you create D, you access the data = of=20 >>> C+A with the functions of D and C, but as soon as you call the function= s=20 >>> inherited from B, B can only access the data of A that are totally in= =20 >>> disuse, that is, create an instance in D generates in memory a variable= "a"=20 >>> with C+A, and also a variable "a" with A , being in class D a C+A, A, w= here=20 >>> the last A is not used, only C+A, in A it ends up using when the functi= ons=20 >>> of B. are called. >>> It is only possible to create a new virtual type function as the only= =20 >>> case to access only C+A, but this generates junk code and in memory it= =20 >>> reserves A as garbage: >>> >>> Code: >>> --------------------------------------- >>> #include >>> >>> class A { >>> public: >>> A(int z_) : z(z_) { } >>> int z; >>> }; >>> >>> class C: public A { >>> public: >>> C(int z_) : A(z_) { } >>> }; >>> >>> class B { >>> public: >>> B() : a(1) { } >>> void f2() { >>> std::cout << "A:" << get_C_a().z << std::endl; >>> } >>> virtual A const& get_C_a() { return a; } >>> A a; // Use only from B >>> }; >>> >>> class D : public B { >>> public: >>> D() : a(3) { } >>> void f2(){ >>> std::cout << "C+A:" << a.z << std::endl; >>> B::f2(); >>> } >>> C a; // Use C+A only from D >>> A const& get_C_a() override { return a; } >>> }; >>> >>> int main() { >>> B b; D d; >>> b.f2(); d.f2(); >>> return 0; >>> } >>> >>> /* OUTPUT: >>> A:1 >>> C+A:3 >>> A:3 >>> */ >>> >>> --------------------------------------- >>> >>> This would be the best option, but not the ideal one. Ideally, "C a;" o= f=20 >>> D replace "A a;" of B, in this way D only uses C+A from "C a;" and B on= ly=20 >>> uses A from "A a;" >>> >>> This is my proposal, a keyword like 'virtual' (or can be any other) in= =20 >>> the variable of the same name that is replaced by the variable definiti= on=20 >>> of the base class. >>> >>> Por ejemplo: >>> Code: >>> --------------------------------------- >>> #include >>> >>> class A { >>> public: >>> A(int z_) : z(z_) { } >>> int z; >>> }; >>> >>> class C: public A { >>> public: >>> C(int z_) : A(z_) { } >>> }; >>> >>> class B { >>> public: >>> B() : a(1) { } >>> void f2() { >>> std::cout << "A:" << a.z << std::endl; >>> } >>> virtual A a; // Use A only from B >>> }; >>> >>> class D : public B { >>> public: >>> D() : a(3) { } >>> void f2(){ >>> std::cout << "C+A:" << a.z << std::endl; >>> B::f2(); >>> } >>> virtual C a; // Use C+A only from D >>> }; >>> >>> int main() { >>> B b; D d; >>> b.f2(); d.f2(); >>> return 0; >>> } >>> >>> /* OUTPUT: >>> A:1 >>> C+A:3 >>> A:3 >>> */ >>> >>> --------------------------------------- >>> >>> well this might not be possible, since compiled the code, the binary=20 >>> code uses the data from an expected position in the variables within th= e=20 >>> classes, so removing it from the list could alter the size and position= of=20 >>> the variables. On the other hand it would be possible, since reserving= =20 >>> memory from A or from C as C+A, generates a group of variables reserved= in=20 >>> memories for each class even if it is C+A and calls functions of A whic= h=20 >>> omits C of C+A Just to have A in view, this could be an advantage. >>> I suggest some other option to simulate a replacement of variable A by = C. >>> If there is a better method that fulfills the same purpose without=20 >>> breaking with the basic structure proposed here then much better. >>> >>> >>> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D >>> >>> Tenemos 2 clases que contienen distintos conjuntos de datos, uno=20 >>> necesita usar las funciones y variables de otra clase, por lo que se=20 >>> incluye como miembro apuntando a la otra clase: >>> >>> member >>> A -------> B >>> >>> Code: >>> --------------------------------------- >>> >>> class A { >>> public: >>> A(int z_) : z(z_) { } >>> int z; >>> }; >>> >>> class B { >>> public: >>> B() : a(1) { } >>> void f2() { >>> std::cout << "A:" << a.z << std::endl; >>> } >>> A a; >>> }; >>> >>> --------------------------------------- >>> >>> Luego se necesita crear una herencia para cada clase, ya que necesita= =20 >>> cubrir una nueva capa de interfaz. Llamemos C y D, donde C usa la clase= =20 >>> base A y D usa la clase base B. >>> >>> member >>> A ---------> B >>> | | >>> |inheritance | inheritance >>> | | >>> v member v >>> C ---------> D >>> >>> Code: >>> --------------------------------------- >>> >>> class A { >>> public: >>> A(int z_) : z(z_) { } >>> int z; >>> }; >>> class C: public A { >>> public: >>> C(int y_) : y(y_), A(y_) { } >>> long y; >>> }; >>> >>> class B { >>> public: >>> B() : a(1) { } >>> void f2() { >>> std::cout << "A:" << a.z << std::endl; >>> } >>> A a; >>> }; >>> class D: public B { >>> public: >>> B() : a(3) { } >>> void f2() { >>> std::cout << "A:" << a.z << std::endl; >>> } >>> C a; >>> }; >>> >>> --------------------------------------- >>> >>> Aqui donde aparecen los problemas, si creas B puedes acceder a los=20 >>> datos de A con las funciones de B. Pero si creas D, accedes a los datos= de=20 >>> C+A con las funciones de D y C, pero tan pronto llamas a las funciones= =20 >>> heredadas de B, B solo puede acceder a los datos de A que estan totalme= nte=20 >>> en desuso, es decir, crear una instancia en D genera en la memoria una= =20 >>> variable "a" con C+A, y tambien una variable "a" con A, siendo en la cl= ase=20 >>> D un C+A,A , donde la ultima A no se usa, solo C+A , en A se termina us= ando=20 >>> cuando se llama a las funciones de B. >>> Solo es posible crear una nueva funcion tipo virtual como unico cas= o=20 >>> para acceder solamente a C+A, pero esto genera codigo basura y en la=20 >>> memoria se reserva A como basura: >>> >>> Code: >>> --------------------------------------- >>> #include >>> >>> class A { >>> public: >>> A(int z_) : z(z_) { } >>> int z; >>> }; >>> >>> class C: public A { >>> public: >>> C(int z_) : A(z_) { } >>> }; >>> >>> class B { >>> public: >>> B() : a(1) { } >>> void f2() { >>> std::cout << "A:" << get_C_a().z << std::endl; >>> } >>> virtual A const& get_C_a() { return a; } >>> A a; // Use only from B >>> }; >>> >>> class D : public B { >>> public: >>> D() : a(3) { } >>> void f2(){ >>> std::cout << "C+A:" << a.z << std::endl; >>> B::f2(); >>> } >>> C a; // Use C+A only from D >>> A const& get_C_a() override { return a; } >>> }; >>> >>> int main() { >>> B b; D d; >>> b.f2(); d.f2(); >>> return 0; >>> } >>> >>> /* OUTPUT: >>> A:1 >>> C+A:3 >>> A:3 >>> */ >>> >>> --------------------------------------- >>> >>> Esta seria la mejor opcion, pero no la ideal. Lo ideal es que "C a;" de= =20 >>> D remplace a "A a;" de B, de esta forma D solo usa C+A de "C a;" y B so= lo=20 >>> usa A de "A a;" >>> >>> Esta es mi propuesta, una palabra clave como 'virtual' (o puede ser=20 >>> cualquier otra) en la variable del mismo nombre que se remplace a la=20 >>> definicion de variable de la clase base. >>> >>> Por ejemplo: >>> Code: >>> --------------------------------------- >>> #include >>> >>> class A { >>> public: >>> A(int z_) : z(z_) { } >>> int z; >>> }; >>> >>> class C: public A { >>> public: >>> C(int z_) : A(z_) { } >>> }; >>> >>> class B { >>> public: >>> B() : a(1) { } >>> void f2() { >>> std::cout << "A:" << a.z << std::endl; >>> } >>> virtual A a; // Use A only from B >>> }; >>> >>> class D : public B { >>> public: >>> D() : a(3) { } >>> void f2(){ >>> std::cout << "C+A:" << a.z << std::endl; >>> B::f2(); >>> } >>> virtual C a; // Use C+A only from D >>> }; >>> >>> >>> >> [snip] >> This problem sounds similar to the "dual inheritance >> hierarchy" problem that this reference: >> >> >> https://pdfs.semanticscholar.org/f403/361d9ef3dac96463787b852b605a918bc4= fe.pdf >> >> addresses. For example, the A and B classes above >> correspond to the B1 and B2 classes in Figure 3 of the above >> reference, and the C and D classes above correspond to the >> D1 and D2 classes in Figure 3 of the above reference. >> >> Is that how it seems to you? >> >> -regards, >> Larry >> >> --=20 You received this message because you are subscribed to the Google Groups "= ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/16c8ccb9-8e42-46cc-9129-52e1129617be%40isocpp.or= g. ------=_Part_1090_899285510.1534002601470 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
La soluci=C3=B3n que me ofrecieron en este lugar fue esta:=

Codigo:
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
class B1
{
public:
=C2=A0 = virtual B2& GetB2() const =3D 0;
};
class B2 {};
class D2 : pu= blic B2 {};
class D1 : public B1
{
public:
=C2=A0 D1(D2& d2= ) : itsD2(d2) {};
=C2=A0 virtual D2& GetB2() const {return itsD2;}private:
=C2=A0 mutable D2& itsD2;
};
=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Pero tiene el problema de que luego necesitas reemplazar todo "itsD2= .." por "GetB2().", esto es una mala practica y solo crea cod= igo basura. Al final es mejor utilizar el lenguaje C en el medio, algo asi = como remplazar estas lineas por las otras siguientes:

Original:
G= etB2().var;
GetB2().var;
GetB2().var;

Mejorado:
D2&d2= =3D*((D2)itsD2);
d2.var;
d2.var;
d2.var;

Es decir, hacer un= a referencia de un "void*itsD2;" desde B1 en lugar de un "mu= table D2&itsD2;" en D1....

la finalidad de esta propuesta e= s utilizar "d2.var" en lugar de "GetB2().var", insisto = en que mi propuesta es la mejor, si no logran mejorar C++ para aceptar el u= so de este tipo de variables entonces voy a insistir en el viejo habito de = C...


El mi=C3=A9rcoles, 25 de julio de 2018, 14:16:43 (UTC-3), r= mb...@gmail.com escribi=C3=B3:
=
Yes, that's exactly what I was looking for!
I did n= ot know that the keyword 'mutable' had to be used, although there i= s still the problem of having to use the virtual function to directly extra= ct the class already converted from a parent class...
The class structur= e that I use is similar, but directly uses a "D2 itsD2;", a direc= t statement within the class itself...

=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D<= br>
si, es justamente lo que estaba buscando!...
no sabia que habia q= ue usar la palabra clave 'mutable', aunque sigue estando el problem= a de tener que usar la funcion virtual para extraer directamente la clase y= a convertida desde una clase padre...
La estructura de clases que yo uso= es similar, pero usa directamente un "D2 itsD2;", una declaraci= =C3=B3n directa dentro de la propia clase...

El mi=C3=A9rcoles, 18 d= e julio de 2018, 7:04:33 (UTC-3), cpplj...@gmail.com escribi=C3=B3:<= blockquote class=3D"gmail_quote" style=3D"margin:0;margin-left:0.8ex;border= -left:1px #ccc solid;padding-left:1ex">


On Monday, = June 11, 2018 at 7:17:54 PM UTC-5, rmb...@gmail.com wrote:
We have 2 classes that conta= in different data sets, one needs to use the functions and variables of ano= ther class, so it is included as a member pointing to the other class:
<= br>=C2=A0=C2=A0 member
A -------> B

Code:
-----------------= ----------------------

class A {
public:
=C2=A0=C2=A0 =C2= =A0A(int z_) : z(z_) {=C2=A0=C2=A0 =C2=A0}
=C2=A0=C2=A0 =C2=A0int z;
= };

class B {
public:
=C2=A0=C2=A0 =C2=A0B() : a(1) { }
=C2= =A0=C2=A0 =C2=A0void f2() {
=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0std::c= out << "A:" << a.z << std::endl;
=C2=A0=C2= =A0 =C2=A0}
=C2=A0=C2=A0 =C2=A0A a;
};

-----------------------= ----------------

Then you need to create an inheritance for eac= h class, since you need to cover a new interface layer. Let's call C an= d D, where C uses the base class A and D uses the base class B.

=C2= =A0=C2=A0 member
A ---------> B
|=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |
|inheritance | inheritance
|=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |
v=C2= =A0 member=C2=A0=C2=A0=C2=A0 v
C ---------> D

Code:
-------= --------------------------------

class A {
public:
=C2=A0= =C2=A0 =C2=A0A(int z_) : z(z_) {=C2=A0=C2=A0 =C2=A0}
=C2=A0=C2=A0 =C2=A0= int z;
};
class C: public A {
public:
=C2=A0=C2=A0 =C2=A0C(int = y_) : y(y_), A(y_) {=C2=A0=C2=A0 =C2=A0}
=C2=A0=C2=A0 =C2=A0long y;
}= ;

class B {
public:
=C2=A0=C2=A0 =C2=A0B() : a(1) { }
=C2= =A0=C2=A0 =C2=A0void f2() {
=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0std::c= out << "A:" << a.z << std::endl;
=C2=A0=C2= =A0 =C2=A0}
=C2=A0=C2=A0 =C2=A0A a;
};
class D: public B {
publ= ic:
=C2=A0=C2=A0 =C2=A0B() : a(3) { }
=C2=A0=C2=A0 =C2=A0void f2() {<= br>=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0std::cout << "A:" = << a.z << std::endl;
=C2=A0=C2=A0 =C2=A0}
=C2=A0=C2=A0 = =C2=A0C a;
};

---------------------------------------
Here where the problems appear, if you create B you can access the data of= A with the functions of B. But if you create D, you access the data of C+A= with the functions of D and C, but as soon as you call the functions inher= ited from B, B can only access the data of A that are totally in disuse, th= at is, create an instance in D generates in memory a variable "a"= with C+A, and also a variable "a" with A , being in class D a C+= A, A, where the last A is not used, only C+A, in A it ends up using when th= e functions of B. are called.
=C2=A0 It is only possible to create a new= virtual type function as the only case to access only C+A, but this genera= tes junk code and in memory it reserves A as garbage:

Code:
-----= ----------------------------------
#include <iostream>
class A {
public:
=C2=A0=C2=A0 =C2=A0A(int z_) : z(z_) {=C2=A0=C2=A0= =C2=A0}
=C2=A0=C2=A0 =C2=A0int z;
};

class C: public A {
p= ublic:
=C2=A0=C2=A0 =C2=A0C(int z_) : A(z_) {=C2=A0=C2=A0 =C2=A0}
};<= br>
class B {
public:
=C2=A0=C2=A0 =C2=A0B() : a(1) { }
=C2=A0= =C2=A0 =C2=A0void f2() {
=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0std::cout= << "A:" << get_C_a().z << std::endl;
=C2=A0= =C2=A0 =C2=A0}
=C2=A0=C2=A0 =C2=A0virtual A const& get_C_a() { retur= n a; }
=C2=A0=C2=A0 =C2=A0A a; // Use only from B
};

class D := public B {
public:
=C2=A0=C2=A0 =C2=A0D() : a(3) { }
=C2=A0=C2=A0= =C2=A0void f2(){
=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0std::cout <&l= t; "C+A:" << a.z << std::endl;
=C2=A0=C2=A0 =C2=A0= =C2=A0=C2=A0 =C2=A0B::f2();
=C2=A0=C2=A0 =C2=A0}
=C2=A0=C2=A0 =C2=A0C= a; // Use C+A only from D
=C2=A0=C2=A0 =C2=A0A const& get_C_a() ove= rride { return a; }
};

int main() {
=C2=A0=C2=A0 =C2=A0B b; D = d;
=C2=A0=C2=A0 =C2=A0b.f2(); d.f2();
=C2=A0=C2=A0 =C2=A0return 0;}

/* OUTPUT:
A:1
C+A:3
A:3
*/

------------------= ---------------------

This would be the best option, but not th= e ideal one. Ideally, "C a;" of D replace "A a;" of B, = in this way D only uses C+A from "C a;" and B only uses A from &q= uot;A a;"

This is my proposal, a keyword like 'virtual'= (or can be any other) in the variable of the same name that is replaced by= the variable definition of the base class.

Por ejemplo:
Code:---------------------------------------
#include <iostream><= br>
class A {
public:
=C2=A0=C2=A0 =C2=A0A(int z_) : z(z_) {=C2=A0= =C2=A0 =C2=A0}
=C2=A0=C2=A0 =C2=A0int z;
};

class C: public A = {
public:
=C2=A0=C2=A0 =C2=A0C(int z_) : A(z_) {=C2=A0=C2=A0 =C2=A0}<= br>};

class B {
public:
=C2=A0=C2=A0 =C2=A0B() : a(1) { }
= =C2=A0=C2=A0 =C2=A0void f2() {
=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0std= ::cout << "A:" << a.z << std::endl;
=C2=A0= =C2=A0 =C2=A0}
=C2=A0=C2=A0 =C2=A0virtual A a; // Use A only from B
}= ;

class D : public B {
public:
=C2=A0=C2=A0 =C2=A0D() : a(3) {= }
=C2=A0=C2=A0 =C2=A0void f2(){
=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2= =A0std::cout << "C+A:" << a.z << std::endl;
= =C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0B::f2();
=C2=A0=C2=A0 =C2=A0}
= =C2=A0=C2=A0 =C2=A0virtual C a; // Use C+A only from D
};

int mai= n() {
=C2=A0=C2=A0 =C2=A0B b; D d;
=C2=A0=C2=A0 =C2=A0b.f2(); d.f2();=
=C2=A0=C2=A0 =C2=A0return 0;
}

/* OUTPUT:
A:1
C+A:3
= A:3
*/

---------------------------------------

well t= his might not be possible, since compiled the code, the binary code uses th= e data from an expected position in the variables within the classes, so re= moving it from the list could alter the size and position of the variables.= On the other hand it would be possible, since reserving memory from A or f= rom C as C+A, generates a group of variables reserved in memories for each = class even if it is C+A and calls functions of A which omits C of C+A Just = to have A in view, this could be an advantage.
I suggest some other opti= on to simulate a replacement of variable A by C.
If there is a better me= thod that fulfills the same purpose without breaking with the basic structu= re proposed here then much better.

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Tenemos 2 clases que contienen distintos conjuntos de datos, uno necesita = usar las funciones y variables de otra clase, por lo que se incluye como mi= embro apuntando a la otra clase:

=C2=A0=C2=A0 member
A ------->= ; B

Code:
---------------------------------------

cla= ss A {
public:
=C2=A0=C2=A0 =C2=A0A(int z_) : z(z_) {=C2=A0=C2=A0 =C2= =A0}
=C2=A0=C2=A0 =C2=A0int z;
};

class B {
public:
=C2= =A0=C2=A0 =C2=A0B() : a(1) { }
=C2=A0=C2=A0 =C2=A0void f2() {
=C2=A0= =C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0std::cout << "A:" << = a.z << std::endl;
=C2=A0=C2=A0 =C2=A0}
=C2=A0=C2=A0 =C2=A0A a;<= br>};

---------------------------------------

Luego se n= ecesita crear una herencia para cada clase, ya que necesita cubrir una nuev= a capa de interfaz. Llamemos C y D, donde C usa la clase base A y D usa la = clase base B.

=C2=A0=C2=A0 member
A ---------> B
|=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |
|inheritance= | inheritance
|=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0 |
v=C2=A0 member=C2=A0=C2=A0=C2=A0 v
C ---------> D
Code:
---------------------------------------

class A = {
public:
=C2=A0=C2=A0 =C2=A0A(int z_) : z(z_) {=C2=A0=C2=A0 =C2=A0}<= br>=C2=A0=C2=A0 =C2=A0int z;
};
class C: public A {
public:
=C2= =A0=C2=A0 =C2=A0C(int y_) : y(y_), A(y_) {=C2=A0=C2=A0 =C2=A0}
=C2=A0=C2= =A0 =C2=A0long y;
};

class B {
public:
=C2=A0=C2=A0 =C2=A0B= () : a(1) { }
=C2=A0=C2=A0 =C2=A0void f2() {
=C2=A0=C2=A0 =C2=A0=C2= =A0=C2=A0 =C2=A0std::cout << "A:" << a.z << std= ::endl;
=C2=A0=C2=A0 =C2=A0}
=C2=A0=C2=A0 =C2=A0A a;
};
class D= : public B {
public:
=C2=A0=C2=A0 =C2=A0B() : a(3) { }
=C2=A0=C2= =A0 =C2=A0void f2() {
=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0std::cout &l= t;< "A:" << a.z << std::endl;
=C2=A0=C2=A0 =C2= =A0}
=C2=A0=C2=A0 =C2=A0C a;
};

------------------------------= ---------

=C2=A0 Aqui donde aparecen los problemas, si creas B = puedes acceder a los datos de A con las funciones de B. Pero si creas D, ac= cedes a los datos de C+A con las funciones de D y C, pero tan pronto llamas= a las funciones heredadas de B, B solo puede acceder a los datos de A que = estan totalmente en desuso, es decir, crear una instancia en D genera en la= memoria una variable "a" con C+A, y tambien una variable "a= " con A, siendo en la clase D un C+A,A , donde la ultima A no se usa, = solo C+A , en A se termina usando cuando se llama a las funciones de B.
= =C2=A0=C2=A0 =C2=A0Solo es posible crear una nueva funcion tipo virtual com= o unico caso para acceder solamente a C+A, pero esto genera codigo basura y= en la memoria se reserva A como basura:

Code:
------------------= ---------------------
#include <iostream>

class A {public:
=C2=A0=C2=A0 =C2=A0A(int z_) : z(z_) {=C2=A0=C2=A0 =C2=A0}
= =C2=A0=C2=A0 =C2=A0int z;
};

class C: public A {
public:
= =C2=A0=C2=A0 =C2=A0C(int z_) : A(z_) {=C2=A0=C2=A0 =C2=A0}
};

cla= ss B {
public:
=C2=A0=C2=A0 =C2=A0B() : a(1) { }
=C2=A0=C2=A0 =C2= =A0void f2() {
=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0std::cout << = "A:" << get_C_a().z << std::endl;
=C2=A0=C2=A0 =C2= =A0}
=C2=A0=C2=A0 =C2=A0virtual A const& get_C_a() { return a; }
= =C2=A0=C2=A0 =C2=A0A a; // Use only from B
};

class D : public B = {
public:
=C2=A0=C2=A0 =C2=A0D() : a(3) { }
=C2=A0=C2=A0 =C2=A0voi= d f2(){
=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0std::cout << "C= +A:" << a.z << std::endl;
=C2=A0=C2=A0 =C2=A0=C2=A0=C2= =A0 =C2=A0B::f2();
=C2=A0=C2=A0 =C2=A0}
=C2=A0=C2=A0 =C2=A0C a; // Us= e C+A only from D
=C2=A0=C2=A0 =C2=A0A const& get_C_a() override { r= eturn a; }
};

int main() {
=C2=A0=C2=A0 =C2=A0B b; D d;
=C2= =A0=C2=A0 =C2=A0b.f2(); d.f2();
=C2=A0=C2=A0 =C2=A0return 0;
}
/* OUTPUT:
A:1
C+A:3
A:3
*/

---------------------------= ------------

Esta seria la mejor opcion, pero no la ideal. Lo i= deal es que "C a;" de D remplace a "A a;" de B, de esta= forma D solo usa C+A de "C a;" y B solo usa A de "A a;"= ;

Esta es mi propuesta, una palabra clave como 'virtual' (o = puede ser cualquier otra) en la variable del mismo nombre que se remplace a= la definicion de variable de la clase base.

Por ejemplo:
Code:---------------------------------------
#include <iostream>=

class A {
public:
=C2=A0=C2=A0 =C2=A0A(int z_) : z(z_) {=C2= =A0=C2=A0 =C2=A0}
=C2=A0=C2=A0 =C2=A0int z;
};

class C: public= A {
public:
=C2=A0=C2=A0 =C2=A0C(int z_) : A(z_) {=C2=A0=C2=A0 =C2= =A0}
};

class B {
public:
=C2=A0=C2=A0 =C2=A0B() : a(1) { }=
=C2=A0=C2=A0 =C2=A0void f2() {
=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2= =A0std::cout << "A:" << a.z << std::endl;
= =C2=A0=C2=A0 =C2=A0}
=C2=A0=C2=A0 =C2=A0virtual A a; // Use A only from = B
};

class D : public B {
public:
=C2=A0=C2=A0 =C2=A0D() : = a(3) { }
=C2=A0=C2=A0 =C2=A0void f2(){
=C2=A0=C2=A0 =C2=A0=C2=A0=C2= =A0 =C2=A0std::cout << "C+A:" << a.z << std::en= dl;
=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0B::f2();
=C2=A0=C2=A0 =C2= =A0}
=C2=A0=C2=A0 =C2=A0virtual C a; // Use C+A only from D
};


[snip]
This problem = sounds similar to the "dual inheritance
hierarchy" problem tha= t this reference:

https://pdfs.semanticscholar.org/f403/361d9ef3dac96463787b852b605a918bc4fe.pdf

addresses.=C2=A0= For example, the A and B classes above
correspond to the B1 and B2 clas= ses in Figure 3 of the above
reference, and the C and D classes above co= rrespond to the
D1 and D2 classes in Figure 3 of the above reference.
Is that how it seems to you?

-regards,
Larry

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+unsubscribe@isocpp.org.
To post to this group, send email to std-proposals@isocpp.org.
To view this discussion on the web visit https://groups.google.= com/a/isocpp.org/d/msgid/std-proposals/16c8ccb9-8e42-46cc-9129-52e1129617be= %40isocpp.org.
------=_Part_1090_899285510.1534002601470-- ------=_Part_1089_674701743.1534002601469-- .