Re: [Boost-users] [bind] [lambda] and [function] in combination witheach other

From: Peter Dimov (pdimov_at_[hidden])
Date: 2007-03-07 10:03:00

Christoph Borgolte wrote:

[...]

> typedef boost::function<bool(const double& ,const double& )>
> CMP_FNC_DBL_DBL;
> typedef boost::function<bool(const double& )> CMP_FNC_DBL;
> typedef std::map<std::string, CMP_FNC_DBL_DBL> FUNCTION_MAP;
>
> int main()
> {
>   FUNCTION_MAP fm;
>   fm["=="] = (boost::lambda::_1 == boost::lambda::_2);
>   fm["!="] = (boost::lambda::_1 != boost::lambda::_2);
>   //...
>
>   CMP_FNC_DBL_DBL fdd = fm["=="];
>   std::cout << fdd(11., 10.) << std::endl; //works
>
>   //Getting a function object via bind
>   CMP_FNC_DBL_DBL fdd2 =  boost::bind(&FUNCTION_MAP::operator[] , fm,
> std::string("=="));

This gives you a fdd2 that returns fm["=="]. It works because fm["=="] is 
convertible to bool, but doesn't really make much sense.

>   //that is what I really need: a CMP_FNC_DBL_DBL bound to a constant
> value

CMP_FNC_DBL fdd3 = bind( fdd, _1, 4.0 ); // ?