...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
"It's not a question of happiness, it's a requirement. Consider the alternative” Doug Horton
As it was indicated previously boost::optional
is the actual type returned by the boost::convert()
main interface:
boost::optional<TypeOut> boost::convert(TypeIn const&, Converter const&);
The signature is functionally-complete and routinely elided during compilation. Still, the following alternative (and arguably more traditional) interface might be potentially more suitable for certain deployment scenarios (or due to personal preferences):
TypeOut convert(TypeIn const&, Converter const&, TypeOut const& fallback_value); TypeOut convert(TypeIn const&, Converter const&, Functor const& fallback_func); TypeOut convert(TypeIn const&, Converter const&, boost::throw_on_failure);
The interface still provides unambiguous behavior and readability, full support for various program flows and various degrees of conversion-failure detection and processing. It can be deployed in a similar fashion as follows:
struct fallback_func { int operator()() const { log("Failed to convert"); return 42; } };
// Error-processing behavior are specified unambiguously and uniformly. // a) i1: Returns the provided fallback value; // b) i2: Calls the provided failure-processing function; // c) i3: Throws an exception. int i1 = convert<int>(str, cnv, fallback_value); int i2 = convert<int>(str, cnv, fallback_func()); try { // Throwing behavior specified explicitly rather than implied. int i3 = convert<int>(str, cnv, boost::throw_on_failure); } catch (boost::bad_optional_access const&) { // Handle failed conversion. }
Still, the described interfaces are convenience wrappers around the main interface which provides the described behavior with:
int m1 = convert<int>(str, cnv).value_or(fallback_value); int m2 = convert<int>(str, cnv).value_or_eval(fallback_func()); int m3 = convert<int>(str, cnv).value();