From: Daniel Walker (daniel.j.walker_at_[hidden])
Date: 2008-06-06 16:58:56
On Fri, Jun 6, 2008 at 4:51 PM, Eric Niebler <eric_at_[hidden]> wrote:
> Daniel Walker wrote:
>>
>> OK, but I was thinking more of user defined function objects. Something like ...
>>
>> struct f_ {
>> template<class> struct result {
>> typedef void type;
>> };
>> template<class T>
>> void operator()(T& t) { ++t; }
>> };
>>
>> int main()
>> {
>> phoenix::function<f_> f;
>> int i = 0;
>> f(i);
>
> That creates a lazy function invocation, but doesn't execute it.
Haha! Thanks.
>
>> assert(i == 1);
>> }
>>
>> Actually, I just tried this and the assertion failed. So, I assume
>> user defined function objects are required to be "pure." Why is that?
>
>
> #include <boost/phoenix/core.hpp>
> #include <boost/phoenix/operator.hpp>
> #include <boost/phoenix/function.hpp>
>
> namespace phoenix = boost::phoenix;
>
> struct f_
> {
> template<class> struct result {
> typedef void type;
> };
> template<class T>
> void operator()(T& t) { ++t; }
> };
>
> int main()
> {
> using phoenix::arg_names::_1;
> phoenix::function<f_> f;
>
> int i = 0;
> f(_1)(i); // OK
> assert(i == 1);
>
> int j = 0;
> //f(j)(); // by value, doesn't compile
> //assert(j == 0);
>
> f(phoenix::ref(j))(); // by ref, OK
> assert(j == 1);
> }
>
Very good! Thanks. I hate "pure" functions. ;-)
Daniel Walker