From fafcca13d8f6c35bd7cce12c7a61301329193aaa Mon Sep 17 00:00:00 2001
From: Sylvain Joubert <joubert.sy@gmail.com>
Date: Tue, 5 Mar 2024 21:57:52 +0100
Subject: [PATCH] Add support for std::optional (#132)

---
 .../program_options/detail/value_semantic.hpp | 20 +++++++++++++++++++
 test/optional_test.cpp                        | 11 ++++++++--
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/include/boost/program_options/detail/value_semantic.hpp b/include/boost/program_options/detail/value_semantic.hpp
index 9531339a34..870ce2fb9e 100644
--- a/include/boost/program_options/detail/value_semantic.hpp
+++ b/include/boost/program_options/detail/value_semantic.hpp
@@ -8,6 +8,10 @@
 
 #include <boost/throw_exception.hpp>
 
+#ifndef BOOST_NO_CXX17_HDR_OPTIONAL
+#   include <optional>
+#endif
+
 // forward declaration
 namespace boost { template<class T> class optional; }
 
@@ -169,6 +173,22 @@ namespace boost { namespace program_options {
         v = boost::any(boost::optional<T>(boost::any_cast<T>(a)));
     }
 
+#ifndef BOOST_NO_CXX17_HDR_OPTIONAL
+    /** Validates std::optional arguments. */
+    template<class T, class charT>
+    void validate(boost::any& v,
+                  const std::vector<std::basic_string<charT> >& s,
+                  std::optional<T>*,
+                  int)
+    {
+        validators::check_first_occurrence(v);
+        validators::get_single_string(s);
+        boost::any a;
+        validate(a, s, (T*)0, 0);
+        v = boost::any(std::optional<T>(boost::any_cast<T>(a)));
+    }
+#endif
+
     template<class T, class charT>
     void 
     typed_value<T, charT>::
diff --git a/test/optional_test.cpp b/test/optional_test.cpp
index b38308e588..cd34ba6e7a 100644
--- a/test/optional_test.cpp
+++ b/test/optional_test.cpp
@@ -7,6 +7,9 @@ namespace po = boost::program_options;
 
 #include <boost/optional.hpp>
 
+#ifndef BOOST_NO_CXX17_HDR_OPTIONAL
+#   include <optional>
+#endif
 #include <string>
 
 #include "minitest.hpp"
@@ -19,9 +22,10 @@ std::vector<std::string> sv(const char* array[], unsigned size)
     return r;
 }
 
+template<template<typename> class OptionalType>
 void test_optional()
 {
-    boost::optional<int> foo, bar, baz;
+    OptionalType<int> foo, bar, baz;
 
     po::options_description desc;
     desc.add_options()
@@ -48,6 +52,9 @@ void test_optional()
 
 int main(int, char*[])
 {
-    test_optional();
+    test_optional<boost::optional>();
+#ifndef BOOST_NO_CXX17_HDR_OPTIONAL
+    test_optional<std::optional>();
+#endif
     return 0;
 }