RE: [boost] new version of smart pointer class templates

From: Brey, Edward D (EdwardDBrey_at_[hidden])
Date: 2002-01-25 14:46:05

I don't think this will work.  There is no implicit conversion between 0
shared_ptr<FILE>, which is a good thing.

On a larger question, what is the design rational for not making the deleter
a template parameter?  This would allow better code factoring, since you
could make a typedef:

typedef shared_ptr<FILE, cfile_deleter> cfile_ptr;

Then cfile_ptr could be used wherever fopen is used, and would eliminate the
danger of forgetting the fclose parameter (which would result in a subtle
resource leak - the file is never closed).

In my opinion, the deleter template parameter should be instantiated on
demand (in dispose()), rather than stored as a member variable, because it
will almost never be desired to change for a given shared_ptr typedef.

In this example, you would have:

struct cfile_deleter {
        void operator()(FILE* f) {if (f) fclose(f);}
}

You need a null check at dispose time given this model, but it doesn't
really cost you anything since it saves you one at allocation time:

cfile_ptr shared_file (const char* name, const char* mode) {
        return cfile_ptr(fopen(name, mode));
}

 -----Original Message-----
From: 	Greg Colvin [mailto:gcolvin_at_[hidden]] 
Sent:	Friday, 25 January 2002 1:18 PM
To:	boost_at_[hidden]
Subject:	Re: [boost] new version of smart pointer class templates

[snip]
    
    shared_ptr<FILE> shared_file (const char* name, const char* mode) {
        if (FILE* p = fopen(name,mode))
            return shared_ptr<FILE>(p,fclose);
        return 0;
    }