Re: [Boost-users] boost::result_of template

Subject: Re: [Boost-users] boost::result_of template
From: Jeffrey Lee Hellrung, Jr. (jeffrey.hellrung_at_[hidden])
Date: 2012-04-13 12:22:57

On Fri, Apr 13, 2012 at 9:15 AM, Jeffrey Lee Hellrung, Jr. <
jeffrey.hellrung_at_[hidden]> wrote:

> On Fri, Apr 13, 2012 at 7:35 AM, John M. Dlugosz <mpbecey7gu_at_[hidden]>wrote:
>
>> The plot thickens:
>>
>>        class Universe : std::tr1::enable_shared_from_**this<Universe> {
>>           const int answer;
>>        public:
>>           Universe (int a) : answer(a) {}
>>           std::string get_answer() const;
>>           void get_nothing() {}
>>           virtual void blahblah(); // !!!
>>           };
>>
>>
>>
>>
>>        Universe u1(42);
>>        foo (&Universe::get_answer, &u1);
>>
>>
>> Regarding my previous post on the definitions of foo,
>> if the class inherits from enable_shared_from this *and* contains a
>> virtual function, then this call to foo doesn't work, giving funny template
>> errors in boost::result_of.
>>
>
> It's really not so funny :)
>
> &Universe::get_answer is not an object supporting function-call syntax, so
> using boost::result_of to query the result of function application is,
> strictly speaking, meaningless. Boost.Bind happens to have special support
> for pointers-to-member-functions, but not all Boost libraries do, since
> it's a relatively simple matter to wrap the pointer in boost::mem_fun
> (note: I've actually forgotten the precise name).
>
> Regarding your initial message, on how to generically get the result type
> of a function object *or* a pointer-to-member-function, you'd need to
> create your own metafunction which dispatches to boost::result_of or
> Boost.FunctionTypes metafunctions depending on whether the argument is a
> pointer-to-member or not.
>
> You could argue that the language should allow function-call syntax on
> pointers-to-member-functions (and pointers-to-member-objects) as it is
> allowed for ponters-to-functions, and...I might sympathize with you.
>
> [snip errors]
>
> HTH,
>
> - Jeff
>
>
Okay, disregard most of this, I checked the Boost.ResultOf implementation
in 1.49.0, it does support pointers-to-members. Sorry, my bad!

- Jeff