Re: [boost] [bind] recursively binding higher-order functional objects fails to compile.

From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2008-02-20 10:31:36

AMDG

Korcan Hussein wrote:
> Sorry about the poor title, it is difficult for me to explain the 
> problem without code so here is a really simple example of what i'm 
> trying to achieve but fails to compile with Boost.Bind:
>
> #include <boost/bind.hpp>
>
> struct FunFn {
>
> 	typedef void result_type;
> 	template < typename Fun >
> 	void operator()(Fun fn) const {
> 		fn();
> 	}
>
> } const Fn;
>
> void g() { std::cout << "hello\n"; }
>
> int main() {
> 	using namespace boost;
>
> 	bind(Fn, bind(Fn, bind(Fn, bind(Fn, ... bind(Fn, g))();
>
> }
>   

This creates a function object that executes:

Fn(Fn(Fn(g())))

Since the inner functions return void, of course it fails.

> I get type deduction errors, however i have found workaround using 
> Boost.Function for the time being:
>
> #include <boost/function.hpp>
>
> ...
> boost::function< void () >
> 	fnN = bind(Fn, g),
> 	fnN-1 = bind(Fn, fnN),
> 	...,
> 	fn1 = bind(Fn, fn2),
> 	fn = bind(Fn, fn1);
>
> bind(Fn, fn)();
>   

In Christ,
Steven Watanabe