[Boost.Parameter] How to Use Named Parameters in a Class Hierarchy?
Dear all, I'm implementing a hierarchy of classes to handle different types of objects. The characteristics of these objects are mostly similar (so I can put them into a container that knows only about the pure abstract base interface type), but some properties are specific to each object types. I plan to use Boost.Parameter for its capability of providing named parameter to these object types. However, I have one problem in this approach: Since Boost.Parameter requires that the function processing the ArgumentPack to be a template, I cannot make it virtual (a member function template cannot be virtual) in my pure abstract base interface. Furthermore, due to the lack of "virtual" member function, I cannot use the base class pointer to provide these named parameters to some subclasses. So my question is: Is there a way to tackle this problem? (Use Boost.Parameter with virtual member functions? Or avoid using Boost.Parameter, but provide a way to access subclass properties that are not know directly via the base class?) Any suggestion is welcomed! Cheers, Freddie -- Wu Yinghui, Freddie Research & Development Senior Software Engineer Volume Interactions Pte Ltd 1 Kim Seng Promenade, #12-01 Great World City East Tower Singapore 237994 Tel: +65 62226962 (Ext 216) Fax: +65 62226215 Email: yhwu@volumeinteractions.com URL: http://www.volumeinteractions.com Important: This message is intended for the recipient(s) addressed above. It contains privileged and confidential information. If you are not the intended recipient, please notify the sender immediately by replying to this message and then delete it from your system. You must not read, copy, use, or disseminate this communication in any form. Thank you.
Wu Yinghui, Freddie wrote:
Dear all,
I'm implementing a hierarchy of classes to handle different types of objects. The characteristics of these objects are mostly similar (so I can put them into a container that knows only about the pure abstract base interface type), but some properties are specific to each object types.
I plan to use Boost.Parameter for its capability of providing named parameter to these object types. However, I have one problem in this approach: Since Boost.Parameter requires that the function processing the ArgumentPack to be a template, I cannot make it virtual (a member function template cannot be virtual) in my pure abstract base interface. Furthermore, due to the lack of "virtual" member function, I cannot use the base class pointer to provide these named parameters to some subclasses.
Depends on what you actually want to do. Perhaps you could use something like the template pattern (pseudo-code): ----- struct Parameters : boost::parameter::parameters< ... > {}; struct Base { BOOST_PARAMETER_MEMFUN(void, Work, 1, 4, Parameters) { DoWork( p[arg1], p[arg2|0], p[arg3|1] ... ); } private: virtual void DoWork(actual, args, goes, here) = 0; }; class Derived : public Base { virtual void DoWork(actual, args, goes, here) { ... use args ... } }; class Derived2 : public Base { virtual void DoWork(actual, args, goes, here) { ... use args ... } }; ----- I've used something similar myself, hope that gives an idea on how to solve your problem. // Johan
"Johan Nilsson" <r.johan.nilsson@gmail.com> writes:
I plan to use Boost.Parameter for its capability of providing named parameter to these object types. However, I have one problem in this approach: Since Boost.Parameter requires that the function processing the ArgumentPack to be a template, I cannot make it virtual (a member function template cannot be virtual) in my pure abstract base interface. Furthermore, due to the lack of "virtual" member function, I cannot use the base class pointer to provide these named parameters to some subclasses.
Depends on what you actually want to do. Perhaps you could use something like the template pattern (pseudo-code):
----- struct Parameters : boost::parameter::parameters< ... > {};
struct Base { BOOST_PARAMETER_MEMFUN(void, Work, 1, 4, Parameters) { DoWork( p[arg1], p[arg2|0], p[arg3|1] ... ); }
private: virtual void DoWork(actual, args, goes, here) = 0; };
class Derived : public Base { virtual void DoWork(actual, args, goes, here) { ... use args ... } };
class Derived2 : public Base { virtual void DoWork(actual, args, goes, here) { ... use args ... } };
-----
I've used something similar myself, hope that gives an idea on how to solve your problem.
Excellent answer. Also, be sure to check out the latest version of Boost.Parameter that is in CVS (and on the release branch). It's considerably easier to use. -- Dave Abrahams Boost Consulting www.boost-consulting.com
participants (3)
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David Abrahams -
Johan Nilsson -
Wu Yinghui, Freddie