cmdopt: print type argument type information

cmdopt.cpp

@@ -149,6 +149,15 @@ null::execute (const char *restrict)
 }
 
 
+//-----------------------------------------------------------------------------
+const std::string&
+null::example (void) const
+{
+    static const std::string EXAMPLE;
+    return EXAMPLE;
+}
+
+
 ///////////////////////////////////////////////////////////////////////////////
 present::present (std::string _name, std::string _description, bool &_data):
     base (std::move (_name), std::move (_description)),
@@ -164,6 +173,15 @@ present::execute (void)
 }
 
 
+//-----------------------------------------------------------------------------
+const std::string&
+present::example (void) const
+{
+    static const std::string EXAMPLE;
+    return EXAMPLE;
+}
+
+
 //-----------------------------------------------------------------------------
 void
 present::finish (void)
@@ -443,12 +461,28 @@ parser::print_help (const int argc,
         exit (0);
 
     // find the longest long form argument so we can set field alignment 
-    auto largest = std::max_element (m_long.begin (),
+    auto largestwidth = std::max_element (
+        m_long.begin (),
         m_long.end (),
-                                     [] (const auto &a, const auto &b) {
-        return std::get<0> (a).size () < std::get<0> (b).size ();
+        [] (const auto &a, const auto &b)
+    {
+        return std::get<std::string> (a).size () < std::get<std::string> (b).size ();
     });
-    int longwidth = std::get<0> (*largest).size ();
+    int longwidth = std::get<std::string> (*largestwidth).size ();
+
+    // find the longest example text
+    auto largestexample = std::max_element (
+        m_options.cbegin (),
+        m_options.cend (),
+        [] (const auto &a, const auto &b)
+    {
+        const auto &example_a = std::get<std::unique_ptr<option::base>> (a)->example ();
+        const auto &example_b = std::get<std::unique_ptr<option::base>> (b)->example ();
+
+        return example_a.size () > example_b.size ();
+    });
+
+    int longexample = std::get<std::unique_ptr<option::base>> (*largestexample)->example ().size ();
 
     // field width requires an alignment. we don't care about preserving
     // state as we're about to bail anyway
@@ -459,8 +493,9 @@ parser::print_help (const int argc,
 
     for (auto &o: m_options) {
         std::cout << '\t'
-                  << '-' << std::get<0> (o) << '\t'
-                  << std::setw (longwidth) << std::get<1> (o) << '\t'
+                  << '-' << std::get<char> (o) << '\t'
+                  << std::setw (longwidth) << std::get<std::string> (o) << '\t'
+                  << std::setw (longexample) << std::get<std::unique_ptr<option::base>> (o)->example () << '\t'
                   << std::setw (0) << std::get<2> (o)->description ()
                   << '\n';
     }

cmdopt.hpp

@@ -38,6 +38,8 @@ namespace util { namespace cmdopt {
             virtual void start   (void);
             virtual void finish  (void);
 
+            virtual const std::string& example (void) const = 0;
+
             const std::string& name (void) const;
             const std::string& description (void) const;
 
@@ -62,6 +64,8 @@ namespace util { namespace cmdopt {
 
             virtual void execute (void) override;
             virtual void execute (const char *restrict) override;
+
+            virtual const std::string& example (void) const override;
         };
 
 
@@ -72,6 +76,8 @@ namespace util { namespace cmdopt {
             using base::execute;
             virtual void execute (void) override;
 
+            virtual const std::string& example (void) const override;
+
             virtual void finish (void) override;
 
         private:
@@ -87,6 +93,8 @@ namespace util { namespace cmdopt {
             using base::execute;
             void execute (const char *restrict) override;
 
+            const std::string& example (void) const override;
+
             T  data (void) const;
             T& data (void);
             T& data (T);

cmdopt.ipp

@@ -21,6 +21,9 @@
 
 #include <sstream>
 
+#include "./introspection.hpp"
+#include "./iterator.hpp"
+
 namespace util { namespace cmdopt {
     ///////////////////////////////////////////////////////////////////////////
     template <typename T>
@@ -53,6 +56,45 @@ namespace util { namespace cmdopt {
     }
 
 
+    //-------------------------------------------------------------------------
+    namespace detail {
+        template <typename T>
+        std::enable_if_t<!std::is_enum<T>::value, const std::string&>
+        value_example (void)
+        {
+            static const std::string EXAMPLE =
+                std::string {"<"} +
+                std::string {to_string<T> ()} +
+                std::string {">"};
+
+            return EXAMPLE;
+        }
+
+        template <typename T>
+        std::enable_if_t<std::is_enum<T>::value, const std::string&>
+        value_example (void)
+        {
+            static const std::string EXAMPLE = [] (void) {
+                std::ostringstream os;
+                std::copy (std::cbegin (enum_values<T>::values),
+                           std::cend   (enum_values<T>::values),
+                           infix_iterator<T> (os, "|"));
+                return os.str ();
+            } ();
+            return EXAMPLE;
+        }
+    }
+
+
+    //-------------------------------------------------------------------------
+    template <typename T>
+    const std::string&
+    option::value<T>::example (void) const
+    {
+        return detail::value_example<T> ();
+    }
+
+
     //-----------------------------------------------------------------------------
     template <typename T>
     T