Give ArgumentParser value semantics

fixes: p-ranav#50

include/argparse.hpp

@@ -380,6 +380,27 @@ class ArgumentParser {
         .implicit_value(true);
   }
 
+  ArgumentParser(ArgumentParser &&) noexcept = default;
+  ArgumentParser &operator=(ArgumentParser &&) & = default;
+
+  ArgumentParser(const ArgumentParser &other)
+      : mProgramName(other.mProgramName),
+        mPositionalArguments(other.mPositionalArguments),
+        mOptionalArguments(other.mOptionalArguments) {
+    for (auto it = begin(mPositionalArguments); it != end(mPositionalArguments);
+         ++it)
+      index_argument(it);
+    for (auto it = begin(mOptionalArguments); it != end(mOptionalArguments);
+         ++it)
+      index_argument(it);
+  }
+
+  ArgumentParser &operator=(const ArgumentParser &other) & {
+    auto tmp = other;
+    std::swap(*this, tmp);
+    return *this;
+  }
+
   // Parameter packing
   // Call add_argument with variadic number of string arguments
   template <typename... Targs> Argument &add_argument(Targs... Fargs) {

test/main.cpp

@@ -12,4 +12,5 @@
 #include <test_invalid_arguments.hpp>
 #include <test_negative_numbers.hpp>
 #include <test_required_arguments.hpp>
-#include <test_issue_37.hpp>
+#include <test_value_semantics.hpp>
+#include <test_issue_37.hpp>

test/test_value_semantics.hpp

@@ -0,0 +1,95 @@
+#pragma once
+#include <argparse.hpp>
+#include <catch.hpp>
+
+TEST_CASE("ArgumentParser is MoveConstructible and MoveAssignable",
+          "[value_semantics]") {
+  GIVEN("a parser that has two arguments") {
+    argparse::ArgumentParser parser("test");
+    parser.add_argument("foo");
+    parser.add_argument("-f");
+
+    WHEN("move construct a new parser from it") {
+      auto new_parser = std::move(parser);
+
+      THEN("the old parser replaces the new parser") {
+        new_parser.parse_args({"test", "bar", "-f", "nul"});
+
+        REQUIRE(new_parser.get("foo") == "bar");
+        REQUIRE(new_parser.get("-f") == "nul");
+      }
+    }
+
+    WHEN("move assign a parser prvalue to it") {
+      parser = argparse::ArgumentParser("test");
+
+      THEN("the old parser is replaced") {
+        REQUIRE_THROWS_AS(parser.parse_args({"test", "bar"}),
+                          std::runtime_error);
+        REQUIRE_THROWS_AS(parser.parse_args({"test", "-f", "nul"}),
+                          std::runtime_error);
+        REQUIRE_NOTHROW(parser.parse_args({"test"}));
+      }
+    }
+  }
+}
+
+TEST_CASE("ArgumentParser is CopyConstructible and CopyAssignable",
+          "[value_semantics]") {
+  GIVEN("a parser that has two arguments") {
+    argparse::ArgumentParser parser("test");
+    parser.add_argument("foo");
+    parser.add_argument("-f");
+
+    WHEN("copy construct a new parser from it") {
+      auto new_parser = parser;
+
+      THEN("the new parser has the old parser's capability") {
+        new_parser.parse_args({"test", "bar", "-f", "nul"});
+
+        REQUIRE(new_parser.get("foo") == "bar");
+        REQUIRE(new_parser.get("-f") == "nul");
+
+        AND_THEN("but does not share states with the old parser") {
+          REQUIRE_THROWS_AS(parser.get("foo"), std::logic_error);
+          REQUIRE_THROWS_AS(parser.get("-f"), std::logic_error);
+        }
+      }
+
+      AND_THEN("the old parser works as a distinct copy") {
+        new_parser.parse_args({"test", "toe", "-f", "/"});
+
+        REQUIRE(new_parser.get("foo") == "toe");
+        REQUIRE(new_parser.get("-f") == "/");
+      }
+    }
+
+    WHEN("copy assign a parser lvalue to it") {
+      argparse::ArgumentParser optional_parser("test");
+      optional_parser.add_argument("-g");
+      parser = optional_parser;
+
+      THEN("the old parser is replaced") {
+        REQUIRE_THROWS_AS(parser.parse_args({"test", "bar"}),
+                          std::runtime_error);
+        REQUIRE_THROWS_AS(parser.parse_args({"test", "-f", "nul"}),
+                          std::runtime_error);
+        REQUIRE_NOTHROW(parser.parse_args({"test"}));
+        REQUIRE_NOTHROW(parser.parse_args({"test", "-g", "nul"}));
+
+        AND_THEN("but does not share states with the other parser") {
+          REQUIRE(parser.get("-g") == "nul");
+          REQUIRE_THROWS_AS(optional_parser.get("-g"), std::logic_error);
+        }
+      }
+
+      AND_THEN("the other parser works as a distinct copy") {
+        REQUIRE_NOTHROW(optional_parser.parse_args({"test"}));
+        REQUIRE_NOTHROW(optional_parser.parse_args({"test", "-g", "nul"}));
+        REQUIRE_THROWS_AS(
+            optional_parser.parse_args({"test", "bar", "-g", "nul"}),
+            std::runtime_error);
+      }
+    }
+  }
+}