Joel de Guzman wrote:
On 5/1/2010 5:18 PM, Jens Mueller wrote:
Hi,
I'm trying out boost:phoenix. Until now I used boost::lambda. I have code written using boost::lambda that returns a boost::function. E.g.
boost::function<float(float)> flog() { using namespace boost::lambda; return bind(static_cast<float(*)(float)>(std::log), _1); }
And with boost::lambda I can reuse the boost::function like this
boost::function<float(float)> func = -bind(flog(), _1);
to build bigger blocks.
But I cannot make it work with boost::phoenix.
boost::function<float(float)> func = -bind(flog(), arg1);
does not compile.
How do I use a boost::function within phoenix? Or what do I need to return instead of a boost::function to reuse it in phoenix? Basically I want to build more complex functions out of simple ones which are returned by some function to hide the internals of the function. I'm using Boost version 1.41.0 and g++ (Debian 4.3.2-1.1) 4.3.2.
It is a known deficiency with phoenix that it does not work well with boost::function the way you are doing it, due to result_of protocol incompatibility. This has been bugging me for some time now. Let me think about an easy fix. In the meantime, I suggest wrapping the boost function call in a generic phoenix::function. Please see this thread:
Such a wrapper should work any boost function if you make it generic.
I see. Thanks. Can I make the wrapper more generic than: template<typename func> struct boostWrapper { template <typename T> struct result { typedef typename func::result_type type; }; // TODO // can't I use an reference here func f1; boostWrapper(func const& f1) : f1(f1) {} typename func::result_type operator()(typename func::arg1_type i) const { return f1(i); } }; template<typename func> boost::phoenix::function<boostWrapper<func> > wrap(func const& f1) { return boostWrapper<func>(f1); } Specifically: How do I handle general n-ary functions? And is it safe to just store a const reference for the boost function? Jens