Re: [Boost-users] Unique parameter values for interfaces

Subject: Re: [Boost-users] Unique parameter values for interfaces
From: Roman Perepelitsa (roman.perepelitsa_at_[hidden])
Date: 2009-05-06 03:02:20

2009/5/6 Ryan McConnehey <mccorywork_at_[hidden]>

> I'm currently trying to fortify my class api by "make interfaces easy to
> use correctly and hard to use incorrectly".  I have a class as follows.
>
> class api
> {
>   api(ConfigName const& configName_, PathName const& pathName_)
>   : m_ConfigName(configName_.value)
>   , m_PathName(pathName_.value)
>   {}
>
>   std::string   m_ConfigName;
>   std::string   m_PathName;
> };
>
> Both ConfigName and PathName are typedef to a template structure as
> follows.
>
> template<typename S>
> struct ParameterValue
> {
>   ParameterValue(S value_) : value(value_) {}
>   S value
> };
>
> typedef ParameterValue<std::string>   ConfigName;
> typedef ParameterValue<std::string>   PathName;
>
> I realized later that this method doesn't prevent the swapping of a
> ConfigName with a PathName parameter.  Since both parameters are typedef to
> the same "type" of ParameterValue they're interchangeable.  Is there a boost
> class, library or C++ idiom that would provide what I'm looking for?  Since
> I'm going to be using this concept for other classes I build, I'd like
> something that would easily create parameter classes to use but not be
> interchangeable with other classes of the same type.  I know that I could do
> this with a macro but I'm leaving that for a last resort.
>
> Ryan
>

Try this:

template<typename S, *int N*>
struct ParameterValue
{
  ParameterValue(S value_) : value(value_) {}
  S value
};

typedef ParameterValue<std::string, *0*>   ConfigName;
typedef ParameterValue<std::string, *1*>   PathName;

Roman Perepelitsa.