Add Argument::store_into() functions

It is possible to bind arguments to a variable storing their value, as an
alternative to explicitly calling ``program.get<T>(arg_name)`` or ``program[arg_name]``

This is currently implementeted for variables of type ``bool`` (this also
implicitly calls ``flag()``), ``int``, ``double``, ``std::string`` and
``std::vector<std::string>``. If the argument is not specified in the command
line, the default value (if set) is set into the variable.

```cpp
bool flagvar = false;
program.add_argument("--flagvar").store_into(flagvar);

int intvar = 0;
program.add_argument("--intvar").store_into(intvar);

double doublevar = 0;
program.add_argument("--doublevar").store_into(doublevar);

std::string strvar;
program.add_argument("--strvar").store_into(strvar);

std::vector<std::string> strvar_repeated;
program.add_argument("--strvar-repeated").append().store_into(strvar_repeated);

std::vector<std::string> strvar_multi_valued;
program.add_argument("--strvar-multi-valued").nargs(2).store_into(strvar_multi_valued);
```

README.md

@@ -26,6 +26,7 @@
           *    [Joining values of repeated optional arguments](#joining-values-of-repeated-optional-arguments)
           *    [Repeating an argument to increase a value](#repeating-an-argument-to-increase-a-value)
           *    [Mutually Exclusive Group](#mutually-exclusive-group)
+     *    [Storing values into variables](#store-into)
      *    [Negative Numbers](#negative-numbers)
      *    [Combining Positional and Optional Arguments](#combining-positional-and-optional-arguments)
      *    [Printing Help](#printing-help)
@@ -315,6 +316,36 @@ foo@bar:/home/dev/$ ./main
 One of the arguments '--first VAR' or '--second VAR' is required
 ```
 
+### Storing values into variables
+
+It is possible to bind arguments to a variable storing their value, as an
+alternative to explicitly calling ``program.get<T>(arg_name)`` or ``program[arg_name]``
+
+This is currently implementeted for variables of type ``bool`` (this also
+implicitly calls ``flag()``), ``int``, ``double``, ``std::string`` and
+``std::vector<std::string>``. If the argument is not specified in the command
+line, the default value (if set) is set into the variable.
+
+```cpp
+bool flagvar = false;
+program.add_argument("--flagvar").store_into(flagvar);
+
+int intvar = 0;
+program.add_argument("--intvar").store_into(intvar);
+
+double doublevar = 0;
+program.add_argument("--doublevar").store_into(doublevar);
+
+std::string strvar;
+program.add_argument("--strvar").store_into(strvar);
+
+std::vector<std::string> strvar_repeated;
+program.add_argument("--strvar-repeated").append().store_into(strvar_repeated);
+
+std::vector<std::string> strvar_multi_valued;
+program.add_argument("--strvar-multi-valued").nargs(2).store_into(strvar_multi_valued);
+```
+
 ### Negative Numbers
 
 Optional arguments start with ```-```. Can ```argparse``` handle negative numbers? The answer is yes!

include/argparse/argparse.hpp

@@ -689,6 +689,57 @@ public:
     return *this;
   }
 
+  auto &store_into(bool &var) {
+    flag();
+    if (m_default_value.has_value()) {
+      var = std::any_cast<bool>(m_default_value);
+    }
+    action([&var](const auto & /*unused*/) { var = true; });
+    return *this;
+  }
+
+  auto &store_into(int &var) {
+    if (m_default_value.has_value()) {
+      var = std::any_cast<int>(m_default_value);
+    }
+    action([&var](const auto &s) {
+      var = details::parse_number<int, details::radix_10>()(s);
+    });
+    return *this;
+  }
+
+  auto &store_into(double &var) {
+    if (m_default_value.has_value()) {
+      var = std::any_cast<double>(m_default_value);
+    }
+    action([&var](const auto &s) {
+      var = details::parse_number<double, details::chars_format::general>()(s);
+    });
+    return *this;
+  }
+
+  auto &store_into(std::string &var) {
+    if (m_default_value.has_value()) {
+      var = std::any_cast<std::string>(m_default_value);
+    }
+    action([&var](const std::string &s) { var = s; });
+    return *this;
+  }
+
+  auto &store_into(std::vector<std::string> &var) {
+    if (m_default_value.has_value()) {
+      var = std::any_cast<std::vector<std::string>>(m_default_value);
+    }
+    action([this, &var](const std::string &s) {
+      if (!m_is_used) {
+        var.clear();
+      }
+      m_is_used = true;
+      var.push_back(s);
+    });
+    return *this;
+  }
+
   auto &append() {
     m_is_repeatable = true;
     return *this;
@@ -852,7 +903,6 @@ public:
     if (!m_is_repeatable && m_is_used) {
       throw std::runtime_error("Duplicate argument");
     }
-    m_is_used = true;
     m_used_name = used_name;
 
     if (m_choices.has_value()) {
@@ -875,6 +925,7 @@ public:
     if (num_args_max == 0) {
       m_values.emplace_back(m_implicit_value);
       std::visit([](const auto &f) { f({}); }, m_action);
+      m_is_used = true;
       return start;
     }
     if ((dist = static_cast<std::size_t>(std::distance(start, end))) >=
@@ -912,9 +963,11 @@ public:
         Argument &self;
       };
       std::visit(ActionApply{start, end, *this}, m_action);
+      m_is_used = true;
       return end;
     }
     if (m_default_value.has_value()) {
+      m_is_used = true;
       return start;
     }
     throw std::runtime_error("Too few arguments for '" +

test/CMakeLists.txt

@@ -49,6 +49,7 @@ file(GLOB ARGPARSE_TEST_SOURCES
     test_repr.cpp
     test_required_arguments.cpp
     test_scan.cpp
+    test_store_into.cpp
     test_stringstream.cpp
     test_version.cpp
     test_subparsers.cpp

test/test_store_into.cpp

@@ -0,0 +1,161 @@
+#ifdef WITH_MODULE
+import argparse;
+#else
+#include <argparse/argparse.hpp>
+#endif
+#include <doctest.hpp>
+
+using doctest::test_suite;
+
+TEST_CASE("Test store_into(bool), flag not specified" *
+          test_suite("store_into")) {
+  argparse::ArgumentParser program("test");
+  bool flag;
+  program.add_argument("--flag").store_into(flag);
+
+  program.parse_args({"./test.exe"});
+  REQUIRE(flag == false);
+}
+
+TEST_CASE("Test store_into(bool), flag specified" *
+          test_suite("store_into")) {
+  argparse::ArgumentParser program("test");
+  bool flag;
+  program.add_argument("--flag").store_into(flag);
+
+  program.parse_args({"./test.exe", "--flag"});
+  REQUIRE(flag == true);
+}
+
+TEST_CASE("Test store_into(int), no default value, non specified" *
+          test_suite("store_into")) {
+  argparse::ArgumentParser program("test");
+  int res = -1;
+  program.add_argument("--int-opt").store_into(res);
+
+  program.parse_args({"./test.exe"});
+  REQUIRE(res == -1);
+}
+
+TEST_CASE("Test store_into(int), default value, non specified" *
+          test_suite("store_into")) {
+  argparse::ArgumentParser program("test");
+  int res = -1;
+  program.add_argument("--int-opt").default_value(3).store_into(res);
+
+  program.parse_args({"./test.exe"});
+  REQUIRE(res == 3);
+}
+
+TEST_CASE("Test store_into(int), default value, specified" *
+          test_suite("store_into")) {
+  argparse::ArgumentParser program("test");
+  int res = -1;
+  program.add_argument("--int-opt").default_value(3).store_into(res);
+
+  program.parse_args({"./test.exe", "--int-opt", "5"});
+  REQUIRE(res == 5);
+}
+
+TEST_CASE("Test store_into(double), no default value, non specified" *
+          test_suite("store_into")) {
+  argparse::ArgumentParser program("test");
+  double res = -1;
+  program.add_argument("--double-opt").store_into(res);
+
+  program.parse_args({"./test.exe"});
+  REQUIRE(res == -1);
+}
+
+TEST_CASE("Test store_into(double), default value, non specified" *
+          test_suite("store_into")) {
+  argparse::ArgumentParser program("test");
+  double res = -1;
+  program.add_argument("--double-opt").default_value(3.5).store_into(res);
+
+  program.parse_args({"./test.exe"});
+  REQUIRE(res == 3.5);
+}
+
+TEST_CASE("Test store_into(double), default value, specified" *
+          test_suite("store_into")) {
+  argparse::ArgumentParser program("test");
+  double res = -1;
+  program.add_argument("--double-opt").default_value(3.5).store_into(res);
+
+  program.parse_args({"./test.exe", "--double-opt", "5.5"});
+  REQUIRE(res == 5.5);
+}
+
+TEST_CASE("Test store_into(string), no default value, non specified" *
+          test_suite("store_into")) {
+  argparse::ArgumentParser program("test");
+  std::string res = "init";
+  program.add_argument("--str-opt").store_into(res);
+
+  program.parse_args({"./test.exe"});
+  REQUIRE(res == "init");
+}
+
+TEST_CASE("Test store_into(string), default value, non specified" *
+          test_suite("store_into")) {
+  argparse::ArgumentParser program("test");
+  std::string res;
+  program.add_argument("--str-opt").default_value("default").store_into(res);
+
+  program.parse_args({"./test.exe"});
+  REQUIRE(res == "default");
+}
+
+TEST_CASE("Test store_into(string), default value, specified" *
+          test_suite("store_into")) {
+  argparse::ArgumentParser program("test");
+  std::string res;
+  program.add_argument("--str-opt").default_value("default").store_into(res);
+
+  program.parse_args({"./test.exe", "--str-opt", "foo"});
+  REQUIRE(res == "foo");
+}
+
+TEST_CASE("Test store_into(vector of string), no default value, non specified" *
+          test_suite("store_into")) {
+  argparse::ArgumentParser program("test");
+  std::vector<std::string> res;
+  program.add_argument("--strvector-opt").append().store_into(res);
+
+  program.parse_args({"./test.exe"});
+  REQUIRE(res == std::vector<std::string>{});
+}
+
+TEST_CASE("Test store_into(vector of string), default value, non specified" *
+          test_suite("store_into")) {
+  argparse::ArgumentParser program("test");
+  std::vector<std::string> res;
+  program.add_argument("--strvector-opt").append().default_value(
+      std::vector<std::string>{"a", "b"}).store_into(res);
+
+  program.parse_args({"./test.exe"});
+  REQUIRE(res == std::vector<std::string>{"a", "b"});
+}
+
+TEST_CASE("Test store_into(vector of string), default value, specified" *
+          test_suite("store_into")) {
+  argparse::ArgumentParser program("test");
+  std::vector<std::string> res;
+  program.add_argument("--strvector-opt").append().default_value(
+      std::vector<std::string>{"a", "b"}).store_into(res);
+
+  program.parse_args({"./test.exe", "--strvector-opt", "foo", "--strvector-opt", "bar"});
+  REQUIRE(res == std::vector<std::string>{"foo", "bar"});
+}
+
+TEST_CASE("Test store_into(vector of string), default value, multi valued, specified" *
+          test_suite("store_into")) {
+  argparse::ArgumentParser program("test");
+  std::vector<std::string> res;
+  program.add_argument("--strvector-opt").nargs(2).default_value(
+      std::vector<std::string>{"a", "b"}).store_into(res);
+
+  program.parse_args({"./test.exe", "--strvector-opt", "foo", "bar"});
+  REQUIRE(res == std::vector<std::string>{"foo", "bar"});
+}