Const-correct ArgumentParser

include/argparse/argparse.hpp

@@ -925,7 +925,7 @@ class ArgumentParser {
    * @throws std::bad_any_cast if the option is not of type T
    */
   template <typename T = std::string>
-  auto present(std::string_view aArgumentName) -> std::optional<T> {
+  auto present(std::string_view aArgumentName) const -> std::optional<T> {
     return (*this)[aArgumentName].present<T>();
   }
 

test/CMakeLists.txt

@@ -28,6 +28,7 @@ file(GLOB ARGPARSE_TEST_SOURCES
     test_append.cpp
     test_compound_arguments.cpp
     test_container_arguments.cpp
+    test_const_correct.cpp
     test_help.cpp
     test_invalid_arguments.cpp
     test_is_used.cpp

test/test_const_correct.cpp

@@ -0,0 +1,27 @@
+#include <argparse/argparse.hpp>
+#include <doctest.hpp>
+
+using doctest::test_suite;
+
+TEST_CASE("ArgumentParser is const-correct after construction and parsing" *
+          test_suite("value_semantics")) {
+  GIVEN("a parser") {
+    argparse::ArgumentParser parser("test");
+    parser.add_argument("--foo", "-f").help("I am foo");
+    parser.add_description("A description");
+    parser.add_epilog("An epilog");
+
+    WHEN("becomes const-qualified") {
+      parser.parse_args({"./main", "--foo", "baz"});
+      const auto const_parser = std::move(parser);
+
+      THEN("only const methods are accessible") {
+        REQUIRE(const_parser.help().str().size() > 0);
+        REQUIRE(const_parser.present<std::string>("--foo"));
+        REQUIRE(const_parser.is_used("-f"));
+        REQUIRE(const_parser.get("-f") == "baz");
+        REQUIRE(const_parser["-f"] == std::string("baz"));
+      }
+    }
+  }
+}