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

On Thu, Aug 27, 2009 at 18:25, Steven Watanabe wrote:

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 #include <string>

void foo1(int i, std::string a); void foo1(int i, boost::function foo );

int main(int argc, char** argv) {  //boost::function 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, boost::mpl::false_);

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

Thank you for this solution ! I'm sure it will help me at some future point in time to resolve issues of this kind. I feel I can't however put this in the interface of my library, It's a very much used function by users and the interface has to be very clear, so no template argument if only two types are accepted. The only solution I see now is renaming the function name. Thanks again, Peter