Allow check if ArgumentParser has parsed values

README.md

@@ -38,6 +38,7 @@
      *    [Parent Parsers](#parent-parsers)
      *    [Subcommands](#subcommands)
      *    [Parse Known Args](#parse-known-args)
+     *    [ArgumentParser in bool Context](#argumentparser-in-bool-context)
      *    [Custom Prefix Characters](#custom-prefix-characters)
      *    [Custom Assignment Characters](#custom-assignment-characters)
 *    [Further Examples](#further-examples)
@@ -848,7 +849,13 @@ int main(int argc, char *argv[]) {
 }
 ```
 
-### Custom Prefix Characters 
+### ArgumentParser in bool Context
+
+An `ArgumentParser` is `false` until it (or one of its subparsers) have extracted
+known value(s) with `.parse_args` or `.parse_known_args`. When using `.parse_known_args`,
+unknown arguments will not make a parser `true`.
+
+### Custom Prefix Characters
 
 Most command-line options will use `-` as the prefix, e.g. `-f/--foo`. Parsers that need to support different or additional prefix characters, e.g. for options like `+f` or `/foo`, may specify them using the `set_prefix_chars()`.
 

include/argparse/argparse.hpp

@@ -1104,6 +1104,21 @@ class ArgumentParser {
     return *this;
   }
 
+  explicit operator bool() const {
+    auto arg_used = std::any_of(m_argument_map.cbegin(),
+                                m_argument_map.cend(),
+                                [](auto &it) {
+                                    return it.second->m_is_used;
+                                });
+    auto subparser_used = std::any_of(m_subparser_used.cbegin(),
+                                      m_subparser_used.cend(),
+                                      [](auto &it) {
+                                          return it.second;
+                                      });
+
+    return m_is_parsed && (arg_used || subparser_used);
+  }
+
   // Parameter packing
   // Call add_argument with variadic number of string arguments
   template <typename... Targs> Argument &add_argument(Targs... f_args) {

test/CMakeLists.txt

@@ -27,6 +27,7 @@ file(GLOB ARGPARSE_TEST_SOURCES
     main.cpp
     test_actions.cpp
     test_append.cpp
+    test_bool_operator.cpp
     test_compound_arguments.cpp
     test_container_arguments.cpp
     test_const_correct.cpp

test/test_bool_operator.cpp

@@ -0,0 +1,85 @@
+#include <argparse/argparse.hpp>
+#include <doctest.hpp>
+
+using doctest::test_suite;
+
+TEST_CASE("ArgumentParser in bool context" *
+          test_suite("argument_parser")) {
+  argparse::ArgumentParser program("test");
+  program.add_argument("cases").remaining();
+
+  program.parse_args({"test"});
+  REQUIRE_FALSE(program);
+
+  program.parse_args({"test", "one", "two"});
+  REQUIRE(program);
+}
+
+TEST_CASE("With subparsers in bool context" * test_suite("argument_parser")) {
+  argparse::ArgumentParser program("test");
+
+  argparse::ArgumentParser cmd_fly("fly");
+  cmd_fly.add_argument("plane");
+
+  argparse::ArgumentParser cmd_soar("soar");
+  cmd_soar.add_argument("direction");
+
+  program.add_subparser(cmd_fly);
+  program.add_subparser(cmd_soar);
+
+  program.parse_args({"test", "fly", "glider"});
+  REQUIRE(program);
+  REQUIRE(cmd_fly);
+  REQUIRE_FALSE(cmd_soar);
+}
+
+TEST_CASE("Parsers remain false with unknown arguments" *
+           test_suite("argument_parser")) {
+  argparse::ArgumentParser program("test");
+
+  argparse::ArgumentParser cmd_build("build");
+  cmd_build.add_argument("--file").nargs(1);
+
+  argparse::ArgumentParser cmd_run("run");
+  cmd_run.add_argument("--file").nargs(1);
+
+  program.add_subparser(cmd_build);
+  program.add_subparser(cmd_run);
+
+  auto unknowns =
+      program.parse_known_args({"test", "badger", "--add-meal", "grubs"});
+  REQUIRE_FALSE(program);
+  REQUIRE_FALSE(cmd_build);
+  REQUIRE_FALSE(cmd_run);
+}
+
+TEST_CASE("Multi-level parsers match subparser bool" *
+           test_suite("argument_parser")) {
+  argparse::ArgumentParser program("test");
+
+  argparse::ArgumentParser cmd_cook("cook");
+  cmd_cook.add_argument("--temperature");
+
+  argparse::ArgumentParser cmd_cook_boil("boil");
+  cmd_cook_boil.add_argument("--rate");
+
+  argparse::ArgumentParser cmd_cook_boil_stir("stir");
+  cmd_cook_boil_stir.add_argument("--rate");
+
+  argparse::ArgumentParser cmd_wash("wash");
+
+  program.add_subparser(cmd_cook);
+  cmd_cook.add_subparser(cmd_cook_boil);
+  cmd_cook_boil.add_subparser(cmd_cook_boil_stir);
+
+  program.add_subparser(cmd_wash);
+
+  auto unknowns = program.parse_known_args(
+      {"test", "cook", "boil", "stir", "--rate", "fast"});
+
+  REQUIRE(program);
+  REQUIRE(cmd_cook);
+  REQUIRE(cmd_cook_boil);
+  REQUIRE(cmd_cook_boil_stir);
+  REQUIRE_FALSE(cmd_wash);
+}