Running into something very strange with boost::lexical_cast in 1.39. This code works, but notice the f(). If I attempt to get rid of it and call boost::lexical_cast directly in the constructor for test I get this error: 1>d:\dev_workspace\experimental\scratch\scratch\main.cpp(16) : error C2783: 'Target boost::lexical_cast(const Source &)' : could not deduce template argument for 'Target' 1> d:\boostvs39\include\boost\lexical_cast.hpp(1164) : see declaration of 'boost::lexical_cast' This is hard for me to understand since I've given the target type as a template parameter....and the f() version works just fine. It even works if I make it inline as the lexical_cast function is. Any ideas? #include <boost/lexical_cast.hpp> #include <string> #include <iostream> template < typename R, typename T > R f(T const& x) { return boost::lexical_cast<R>(x); } template < typename T > struct test { test(std::string const& x = f<std::string>(T())) : test_string(x) {} std::string test_string; }; int main() { test<int> t; std::cout << t.test_string; std::cout << boost::lexical_cast<std::string>(int()); std::cin.get(); }