Re: [Boost-users] boost::function unusable as overloadable function argument

Subject: Re: [Boost-users] boost::function unusable as overloadable function argument
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-08-27 12:25:27

AMDG

Peter Soetens wrote:
> I had this situation in a bigger program, where a user could supply a
> string or a function object:
>
> <code>
> #include <boost/function.hpp>
> #include <string>
>
> void foo1(int i, std::string a);
> void foo1(int i, boost::function<void(void)> foo );
>
> int main(int argc, char** argv)
> {
>   //boost::function<void(void)> foo = "hello"; // this line won't compile
>
>   foo1( 3, "hello" ); //error: call of overloaded ‘foo1(int, const
> char [6])’ is ambiguous
>
>   return 0;
> }
> </code>
>
>
> Although constructing a boost::function from a C string is nonsense,
> the compiler does consider it as an alternative when trying to find
> the right foo1. Is there any work around to keep the overloads without
> requiring the user to write
> foo1(3, string("hello")); or is this a compiler bug (g++ (Ubuntu
> 4.3.3-5ubuntu4) 4.3.3)?
>   

You can use tag dispatching:

void foo1_impl(int, std::string a, boost::mpl::true_);
void foo1_impl(int, boost::function<void(void)>, boost::mpl::false_);

template<class T>
void foo1(int i, T t) {
    foo1_impl(i, t, boost::is_convertible<T, std::string>());
};

In Christ,
Steven Watanabe