Subject: Re: [boost] Formal Review Request: TypeErasure
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2012-06-19 00:12:15
AMDG
On 06/18/2012 12:25 PM, lcaminiti wrote:
>
> lcaminiti wrote
>>
>> I will use the lib in some use cases that I ran into the past and let you
>> know if I find a nice example not too complex (I don't remember what the
>> use cases were but they were about type erasure).
>>
>
> Is this a sensible use of this library or is there a much better way to do
> the following?
>
This is a textbook use case for the library.
Use TypeErasure states the intent of the code clearly.
obj_ can hold any type that is CopyConstructible,
and Ostreamable. (you don't actually need typeid_ here).
>
> #include <boost/type_erasure/any.hpp>
> #include <boost/type_erasure/builtin.hpp>
> #include <boost/type_erasure/operators.hpp>
> #include <boost/mpl/vector.hpp>
> #include <iostream>
>
> struct display
> {
> public: template< typename T >
> explicit display ( T const& obj ) : obj_(obj) {}
>
> public: void print ( void ) { std::cout << obj_ << std::endl; }
>
> public: boost::type_erasure::any<
> boost::mpl::vector<
> boost::type_erasure::copy_constructible<>
> , boost::type_erasure::typeid_<>
> , boost::type_erasure::ostreamable<>
> >
> > obj_;
> };
>
> int main ( void )
> {
> display i(-1), d('x');
> i.print();
> d.print();
> return 0;
> }
>
> I had to do something like this in the past where:
> 1. I didn't want display to be a template but I wanted it to handle generic
> types as passed to the constructor.
> 2. I knew a-priori the operations that display needed from T (e.g.,
> operator<<).
> 3. I had to store the object of the generic type T so the operation on T
> could be performed later (e.g., by print).
> I needed to do this as an implementation detail so the original problem I
> was trying to solve has little relevance in general. But I wanted to ask if
> using this library is a reasonable approach to do the above of it there are
> better ways.
>
In Christ,
Steven Watanabe