Refined to_string for variant

Author: hsutter

include/cpp2util.h

@@ -800,10 +800,7 @@ inline auto to_string(std::variant<Ts...> const& v) -> std::string
  if constexpr (is_any<std::monostate, Ts...>) if (std::get_if<std::monostate>(&v) != nullptr) return "(empty)";
 
  return std::visit([](auto&& arg) -> std::string {
- if constexpr (requires { cpp2::to_string(arg); }) {
- return cpp2::to_string(arg);
- }
- return "";
+ return cpp2::to_string(arg);
  }, v);
 }
 

regression-tests/mixed-string-interpolation.cpp2

@@ -46,6 +46,8 @@ main: () -> int = {
 
  vv: std::variant<int, std::string, std::pair<int, double> > = ();
  std::cout << "vv = (vv)$\n";
+ vv = std::make_pair(1,2.3);
+ std::cout << "vv = (vv)$\n";
 
  std::cout << "custom = (custom)$\n";
 }

regression-tests/test-results/mixed-string-interpolation.cpp

@@ -56,6 +56,8 @@ struct custom_struct_with_no_stringize_customization { } custom;
 
  std::variant<int,std::string,std::pair<int,double>> vv { }; 
  std::cout << "vv = " + cpp2::to_string(vv) + "\n";
+ vv = std::make_pair(1, 2.3);
+ std::cout << "vv = " + cpp2::to_string(vv) + "\n";
 
  std::cout << "custom = " + cpp2::to_string(custom) + "\n";
 }