use std::variant instead of boost::variant

NEWS.md

@@ -37,7 +37,8 @@
   library will be used if found via `pkg-config`. If it is found, support for
   reading chapters from DVDs will be enabled in `mkvmerge` and the MKVToolNix
   GUI. Part of the implementation of #2808.
-* Boost's Date/Time, Range and Range Adaptors libraries are not used anymore.
+* Boost's Date/Time, Range, Range Adaptors, Tri-Bool, Variant libraries are
+  not used anymore.
 
 
 # Version 46.0.0 "No Deeper Escape" 2020-05-01

README.md

@@ -96,8 +96,8 @@ programs and libraries you absolutely need are:
 - [zlib](http://www.zlib.net/) — a compression library
 
 - [Boost](http://www.boost.org/) — Several of Boost's libraries are
-  used: `filesystem`, `system`, `math`, `operators`, `rational`,
-  `variant`. At least v1.60.0 is required.
+  used: `filesystem`, `system`, `math`, `operators`, `rational`. At
+  least v1.60.0 is required.
 
 - [libxslt's xsltproc binary](http://xmlsoft.org/libxslt/) and
   [DocBook XSL stylesheets](https://sourceforge.net/projects/docbook/files/docbook-xsl/)

ac/boost.m4

@@ -26,7 +26,3 @@ AX_BOOST_CHECK_HEADERS([boost/lexical_cast.hpp],,[
 AX_BOOST_CHECK_HEADERS([boost/operators.hpp],,[
   AC_MSG_ERROR([Boost's Operators library is required but wasn't found])
 ])
-
-AX_BOOST_CHECK_HEADERS([boost/variant.hpp],,[
-  AC_MSG_ERROR([Boost's variant library is required but wasn't found])
-])

src/common/amf.cpp

@@ -19,6 +19,24 @@
 
 namespace mtx::amf {
 
+namespace {
+
+std::string
+value_to_string(value_type_t const &value) {
+  if (std::holds_alternative<double>(value))
+    return fmt::format("{0}", std::get<double>(value));
+
+  if (std::holds_alternative<bool>(value))
+    return std::get<bool>(value) ? "yes" : "no";
+
+  if (std::holds_alternative<std::string>(value))
+    return std::get<std::string>(value);
+
+  return {};
+}
+
+}
+
 script_parser_c::script_parser_c(memory_cptr const &mem)
   : m_data_mem{mem}
   , m_data{*mem.get()}
@@ -62,7 +80,7 @@ script_parser_c::read_properties(std::unordered_map<std::string, value_type_t> &
     auto key   = read_string(TYPE_STRING);
     auto value = read_value();
 
-    mxdebug_if(m_debug, fmt::format("{0}Property key: {1}; value read: {2}; value: {3}\n", level_spacer(), key, value.second, boost::apply_visitor(value_to_string_c(), value.first)));
+    mxdebug_if(m_debug, fmt::format("{0}Property key: {1}; value read: {2}; value: {3}\n", level_spacer(), key, value.second, value_to_string(value.first)));
 
     if (key.empty() || !value.second)
       break;
@@ -99,7 +117,7 @@ script_parser_c::read_value() {
 
   else if ((TYPE_STRING == data_type) || (TYPE_LONG_STRING == data_type)) {
     value = read_string(data_type);
-    m_in_meta_data = boost::get<std::string>(value) == "onMetaData";
+    m_in_meta_data = std::get<std::string>(value) == "onMetaData";
 
   } else if (TYPE_OBJECT == data_type) {
     std::unordered_map<std::string, value_type_t> dummy;

src/common/amf.h

@@ -16,30 +16,15 @@
 #include "common/common_pch.h"
 
 #include <unordered_map>
-#include <boost/variant.hpp>
+#include <variant>
 
 #include "common/mm_mem_io.h"
 
 namespace mtx::amf {
 
-using value_type_t = boost::variant<double, bool, std::string>;
+using value_type_t = std::variant<double, bool, std::string>;
 using meta_data_t  = std::unordered_map<std::string, value_type_t>;
 
-class value_to_string_c: public boost::static_visitor<std::string> {
-public:
-  std::string operator ()(double value) const {
-    return fmt::format("{0}", value);
-  }
-
-  std::string operator ()(bool value) const {
-    return value ? "yes" : "no";
-  }
-
-  std::string operator ()(std::string const &value) const {
-    return value;
-  }
-};
-
 class script_parser_c {
 public:
   enum data_type_e {
@@ -74,13 +59,13 @@ public:
   meta_data_t const &get_meta_data() const;
 
   template<typename T>
-  T const *
+  std::optional<T>
   get_meta_data_value(std::string const &key) {
     auto itr = m_meta_data.find(key);
     if (m_meta_data.end() == itr)
-      return nullptr;
+      return {};
 
-    return boost::get<T>(&itr->second);
+    return std::get<T>(itr->second);
   }
 
 protected:

src/input/r_flv.cpp

@@ -680,7 +680,7 @@ flv_reader_c::process_script_tag() {
     mtx::amf::script_parser_c parser{m_in->read(m_tag.m_data_size)};
     parser.parse();
 
-    double const *number;
+    std::optional<double> number;
 
     if ((number = parser.get_meta_data_value<double>("framerate"))) {
       m_tracks[m_video_track_idx]->m_v_frame_rate = *number;