format: allow implicit conversion from formats to strings

format.hpp

@@ -104,17 +104,32 @@ namespace cruft::format {
         /// lifetime of the return value.
         template <typename ...Args>
         bound<Args...>
-        operator () (const Args &...args) &;
+        operator() (const Args &...args) &;
 
         /// records a complete collection of parameters for rendering in the
         /// future. takes ownership of the specifiers so there is no lifetime
         /// requirement.
         template <typename ...Args>
         stored<Args...>
-        operator () (const Args &...args) &&;
+        operator() (const Args &...args) &&;
     };
 
 
+    template <typename... ValueT>
+    class bound;
+
+    template <typename ...Args>
+    std::string
+    to_string (const bound<Args...>&);
+
+    template <typename... ValueT>
+    class stored;
+
+    template <typename ...Args>
+    std::string
+    to_string (const bound<Args...>&);
+
+
     /// parameter collection for a non-owning sequence of specifiers
     template <typename ...ValueT>
     class bound {
@@ -124,13 +139,21 @@ namespace cruft::format {
             m_values {args...}
         { ; }
 
+
         auto specifiers (void) const
         { return view (m_parsed.m_specifiers); }
 
+
         template <size_t Index>
         auto
         get (void) const& { return std::get<Index> (m_values); }
 
+
+        operator ::std::string () const
+        {
+            return to_string (*this);
+        }
+
     private:
         const parsed &m_parsed;
         std::tuple<const ValueT&...> m_values;
@@ -146,16 +169,24 @@ namespace cruft::format {
             m_values {args...}
         { ; }
 
+
         auto
         specifiers (void) const&
         {
             return view {m_specifiers};
         }
 
+
         template <size_t Index>
         const auto&
         get (void) const& { return std::get<Index> (m_values); }
 
+
+        operator ::std::string () const
+        {
+            return to_string (*this);
+        }
+
     private:
         std::vector<specifier> m_specifiers;
         std::tuple<const ValueT&...> m_values;
@@ -164,13 +195,13 @@ namespace cruft::format {
 
     template <typename ...Args>
     bound<Args...>
-    parsed::operator () (const Args &...args) &
+    parsed::operator() (const Args &...args) &
     { return bound { *this, args... }; }
 
 
     template <typename ...Args>
     stored<Args...>
-    parsed::operator () (const Args &...args) &&
+    parsed::operator() (const Args &...args) &&
     {
         return stored { std::move (m_specifiers), args... };
     }