Text output support added for quantity

src/include/units/bits/fixed_string.h

@@ -21,6 +21,7 @@
 // SOFTWARE.
 
 #include <cstdlib>
+#include <ostream>
 
 namespace units {
 
@@ -68,6 +69,12 @@ namespace units {
       }
       return first1 == last1 && first2 != last2;
     }
+
+    template<class Traits>
+    friend std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, const basic_fixed_string& txt)
+    {
+      return os << txt.c_str();
+    }
   };
 
   template<typename CharT, std::size_t N>

src/include/units/format.h

@@ -0,0 +1,106 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Mateusz Pusz
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#pragma once
+
+#include <units/quantity.h>
+
+namespace units {
+
+  namespace detail {
+
+    template<typename Ratio, typename CharT, typename Traits>
+    void print_ratio(std::basic_ostream<CharT, Traits>& os)
+    {
+      if constexpr(Ratio::num != 1 || Ratio::den != 1) {
+        if constexpr(Ratio::den == 1) {
+          os << "[" << Ratio::num << "]";
+        }
+        else {
+          os << "[" << Ratio::num << "/" << Ratio::den << "]";
+        }
+      }
+    }
+
+    template<typename Ratio>
+    inline constexpr std::string_view ratio_txt = "";
+
+    template<> inline constexpr std::string_view ratio_txt<ratio<1, std::atto::den>> = "a";
+    template<> inline constexpr std::string_view ratio_txt<ratio<1, std::femto::den>> = "f";
+    template<> inline constexpr std::string_view ratio_txt<ratio<1, std::pico::den>> = "p";
+    template<> inline constexpr std::string_view ratio_txt<ratio<1, std::nano::den>> = "n";
+    template<> inline constexpr std::string_view ratio_txt<ratio<1, std::micro::den>> = "\u00b5\u0073";
+    template<> inline constexpr std::string_view ratio_txt<ratio<1, std::milli::den>> = "m";
+    template<> inline constexpr std::string_view ratio_txt<ratio<1, std::centi::den>> = "c";
+    template<> inline constexpr std::string_view ratio_txt<ratio<1, std::deci::den>> = "d";
+    template<> inline constexpr std::string_view ratio_txt<ratio<std::deca::num>> = "da";
+    template<> inline constexpr std::string_view ratio_txt<ratio<std::hecto::num>> = "h";
+    template<> inline constexpr std::string_view ratio_txt<ratio<std::kilo::num>> = "k";
+    template<> inline constexpr std::string_view ratio_txt<ratio<std::mega::num>> = "M";
+    template<> inline constexpr std::string_view ratio_txt<ratio<std::giga::num>> = "G";
+    template<> inline constexpr std::string_view ratio_txt<ratio<std::tera::num>> = "T";
+    template<> inline constexpr std::string_view ratio_txt<ratio<std::peta::num>> = "P";
+    template<> inline constexpr std::string_view ratio_txt<ratio<std::exa::num>> = "E";
+
+    template<typename Ratio, typename CharT, typename Traits>
+    void print_prefix_or_ratio(std::basic_ostream<CharT, Traits>& os)
+    {
+      if constexpr(Ratio::num != 1 || Ratio::den != 1) {
+        constexpr auto prefix = ratio_txt<Ratio>;
+
+        if constexpr(prefix != "") {
+          // print as a prefixed unit
+          os << prefix;
+        }
+        else {
+          // print as a ratio of the coherent unit
+          print_ratio<Ratio>(os);
+        }
+      }
+    }
+
+    template<typename CharT, typename Traits, typename... Es>
+    void print_dimensions(std::basic_ostream<CharT, Traits>& os, dimension<Es...>)
+    {
+      bool first = true;
+      auto ingr_printer = [&]<typename E>(E) {
+        if constexpr(E::num < 0) {
+          os << (first ? "1/" : "/");
+        }
+        else {
+          os << (first ? "" : "*");
+        }
+        os << E::dimension::symbol;
+        if constexpr(E::den != 1) {
+          os << "^(" << abs(E::num) << "/" << E::den << ")";
+        }
+        else if constexpr(abs(E::num) != 1) {
+          os << "^" << abs(E::num);
+        }
+        first = false;
+      };
+      (ingr_printer(Es{}), ...);
+    }
+
+  }
+
+}  // namespace units

src/include/units/quantity.h

@@ -24,7 +24,9 @@
 
 #include <units/bits/concepts.h>
 #include <units/unit.h>
+#include <units/format.h>
 #include <limits>
+#include <ostream>
 
 namespace units {
 
@@ -275,6 +277,37 @@ namespace units {
       value_ %= q.count();
       return *this;
     }
+
+    template<class CharT, class Traits>
+    friend std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, const quantity& q)
+    {
+      os << q.count() << " ";
+      if constexpr(!detail::is_unit<quantity::unit>) {
+        // print user-defined unit
+        os << unit::symbol::c_str();
+      }
+      else {
+        using ratio = quantity::unit::ratio;
+        using dim = quantity::unit::dimension;
+        if constexpr(!detail::is_dimension<dim>) {
+          // print as a prefix or ratio of a coherent unit
+          detail::print_prefix_or_ratio<ratio>(os);
+
+          if constexpr(!detail::is_dimension<dim>) {
+            // print coherent unit symbol defined by the user
+            os << downcast_target<units::unit<dim>>::symbol::c_str();
+          }
+        }
+        else {
+          // print as a ratio of a coherent unit
+          detail::print_ratio<ratio>(os);
+
+          // print coherent unit dimensions and their exponents
+          detail::print_dimensions(os, dim{});
+        }
+      }
+      return os;
+    }
   };
 
   template<typename U1, typename Rep1, typename U2, typename Rep2>
@@ -442,9 +475,3 @@ namespace units {
   }
 
 }  // namespace units
-
-
-// template<class charT, class traits, class Rep, class Period>
-// basic_ostream<charT, traits>&
-// operator<<(basic_ostream<charT, traits>& os,
-// const duration<Rep, Period>& d);