RE: [boost] Deriving the type of a value in a class template

From: Stewart, Robert (stewart_at_[hidden])
Date: 2001-11-08 11:55:44

> From: Jim Patterson [mailto:jimp_at_[hidden]]
> 
> I have recently written a template class to manage "C" style handles
> for use in a C++ programs that use "C" libraries.  An example of its
> use is:
> 
> #include "C_HandleManager.hpp"
> 
> #include <iostream>
> #include <cstdlib>
> 
> using namespace std;
> 
> int
> main( int, char** )
> {
>     cout << "starting..." << flush;
>     {
>         C_HandleManager<void*,void,free> memory( malloc(1000) );
>         if ( NULL == memory )
>         {
>             cerr << "\nUnable to allocate memory!" << endl;
>             memory.no_deallocate_reset();
>             return 1;
>         }
> 
>         memset( memory, 0, 1000 );
>     } // memory is destroyed here (and free is called on the pointer)
> 
>     cout << "\ndone!" << endl;
> }

While it may be handy to have a generic class to handle the majority of the
work, I'd think it better to have classes for each case as you encounter it.
That class could inherit from C_HandleManager or even contain one, but it
would be distinct.

> The class looks like:
> template<typename T,        // Type of the handle
>          typename R,        // Return type of the dealloc function
>          R (*DEALLOC)(T)>   // Function to dealloc the handle
> class C_HandleManager;

Sean was asking for something akin to your class being like this:

template <typename Function>
class C_HandleManager;

...
C_HandleManager<free> memory(malloc(1000));

This would, in an ideal world, automatically deduce your T and R from your
DEALLOC (my Function).  That, I think could only be done via a "make"
function that returns an object of the class suitably parameterized.

Rob
Susquehanna International Group, LLP
http://www.sig.com

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