Issue #339 (#348)

* add an example where the name of the enum is printed through a stream output function, which subverted the checkTransformer conversion and prevented conversion of the enumeration.

* add missing 'typename'

* try a simpler version of the value_string using const reference for all overloads

* use auto return type to match to_string return type in value_string

* remove extra spaces

examples/CMakeLists.txt

@@ -203,6 +203,11 @@ add_test(NAME enum_fail COMMAND enum -l 4)
 set_property(TEST enum_fail PROPERTY PASS_REGULAR_EXPRESSION
     "--level: Check 4 value in {" "FAILED")
 
+add_cli_exe(enum_ostream enum_ostream.cpp)
+add_test(NAME enum_ostream_pass COMMAND enum_ostream --level medium)
+set_property(TEST enum_ostream_pass PROPERTY PASS_REGULAR_EXPRESSION
+    "Enum received: Medium")
+
 add_cli_exe(digit_args digit_args.cpp)
 add_test(NAME digit_args COMMAND digit_args -h)
 set_property(TEST digit_args PROPERTY PASS_REGULAR_EXPRESSION

examples/enum_ostream.cpp

@@ -0,0 +1,41 @@
+#include <CLI/CLI.hpp>
+
+enum class Level : int { High, Medium, Low };
+
+// this breaks the code
+inline std::ostream &operator<<(std::ostream &o, const Level &l) {
+    switch(l) {
+    case Level::High:
+        o << "High";
+        break;
+    case Level::Medium:
+        o << "Medium";
+        break;
+    case Level::Low:
+        o << "Low";
+        break;
+    }
+    return o;
+}
+
+int main(int argc, char **argv) {
+    CLI::App app;
+
+    Level level;
+    // specify string->value mappings
+    std::vector<std::pair<std::string, Level>> map{
+        {"high", Level::High}, {"medium", Level::Medium}, {"low", Level::Low}};
+    // checked Transform does the translation and checks the results are either in one of the strings or one of the
+    // translations already
+    app.add_option("-l,--level", level, "Level settings")
+        ->required()
+        ->transform(CLI::CheckedTransformer(map, CLI::ignore_case));
+
+    CLI11_PARSE(app, argc, argv);
+
+    // CLI11's built in enum streaming can be used outside CLI11 like this:
+    using namespace CLI::enums;
+    std::cout << "Enum received: " << level << std::endl;
+
+    return 0;
+}

include/CLI/TypeTools.hpp

@@ -259,6 +259,22 @@ template <typename T1,
 std::string checked_to_string(T &&) {
     return std::string{};
 }
+/// get a string as a convertible value for arithmetic types
+template <typename T, enable_if_t<std::is_arithmetic<T>::value, detail::enabler> = detail::dummy>
+std::string value_string(const T &value) {
+    return std::to_string(value);
+}
+/// get a string as a convertible value for enumerations
+template <typename T, enable_if_t<std::is_enum<T>::value, detail::enabler> = detail::dummy>
+std::string value_string(const T &value) {
+    return std::to_string(static_cast<typename std::underlying_type<T>::type>(value));
+}
+/// for other types just use the regular to_string function
+template <typename T,
+          enable_if_t<!std::is_enum<T>::value && !std::is_arithmetic<T>::value, detail::enabler> = detail::dummy>
+auto value_string(const T &value) -> decltype(to_string(value)) {
+    return to_string(value);
+}
 
 /// This will only trigger for actual void type
 template <typename T, typename Enable = void> struct type_count { static const int value{0}; };

include/CLI/Validators.hpp

@@ -709,7 +709,7 @@ class IsMember : public Validator {
             if(res.first) {
                 // Make sure the version in the input string is identical to the one in the set
                 if(filter_fn) {
-                    input = detail::to_string(detail::pair_adaptor<element_t>::first(*(res.second)));
+                    input = detail::value_string(detail::pair_adaptor<element_t>::first(*(res.second)));
                 }
 
                 // Return empty error string (success)
@@ -778,7 +778,7 @@ class Transformer : public Validator {
             }
             auto res = detail::search(mapping, b, filter_fn);
             if(res.first) {
-                input = detail::to_string(detail::pair_adaptor<element_t>::second(*res.second));
+                input = detail::value_string(detail::pair_adaptor<element_t>::second(*res.second));
             }
             return std::string{};
         };
@@ -846,12 +846,12 @@ class CheckedTransformer : public Validator {
                 }
                 auto res = detail::search(mapping, b, filter_fn);
                 if(res.first) {
-                    input = detail::to_string(detail::pair_adaptor<element_t>::second(*res.second));
+                    input = detail::value_string(detail::pair_adaptor<element_t>::second(*res.second));
                     return std::string{};
                 }
             }
             for(const auto &v : detail::smart_deref(mapping)) {
-                auto output_string = detail::to_string(detail::pair_adaptor<element_t>::second(v));
+                auto output_string = detail::value_string(detail::pair_adaptor<element_t>::second(v));
                 if(output_string == input) {
                     return std::string();
                 }