diff --git a/test/test_append.cpp b/test/test_append.cpp
index bd868ef..005bd92 100644
--- a/test/test_append.cpp
+++ b/test/test_append.cpp
@@ -26,7 +26,7 @@ TEST_CASE("Two int .append" * test_suite("append")) {
   argparse::ArgumentParser program("test");
   program.add_argument("--factor")
     .append()
-    .action([](auto s) { return stoi(s); });
+    .scan<'i', int>();
   program.parse_args({ "test", "--factor", "2", "--factor", "5" });
   auto result { program.get<std::vector<int>>("--factor") };
   REQUIRE(result.at(0) == 2);
diff --git a/test/test_compound_arguments.cpp b/test/test_compound_arguments.cpp
index 7f67547..dd19344 100644
--- a/test/test_compound_arguments.cpp
+++ b/test/test_compound_arguments.cpp
@@ -38,7 +38,7 @@ TEST_CASE("Parse compound toggle arguments with implicit values and nargs" *
 
   program.add_argument("-c")
     .nargs(2)
-    .action([](const std::string& value) { return std::stof(value); });
+    .scan<'g', float>();
 
   program.add_argument("--input_files")
     .nargs(3);
@@ -65,7 +65,7 @@ TEST_CASE("Parse compound toggle arguments with implicit values and nargs and "
 
   program.add_argument("numbers")
     .nargs(3)
-    .action([](const std::string& value) { return std::stoi(value); });
+    .scan<'i', int>();
 
   program.add_argument("-a")
     .default_value(false)
@@ -77,7 +77,7 @@ TEST_CASE("Parse compound toggle arguments with implicit values and nargs and "
 
   program.add_argument("-c")
     .nargs(2)
-    .action([](const std::string& value) { return std::stof(value); });
+    .scan<'g', float>();
 
   program.add_argument("--input_files")
     .nargs(3);
@@ -99,7 +99,7 @@ TEST_CASE("Parse out-of-order compound arguments" *
 
   program.add_argument("-c")
     .nargs(2)
-    .action([](const std::string& value) { return std::stof(value); });
+    .scan<'g', float>();
 
   program.parse_args({ "./main", "-cab", "3.14", "2.718" });
 
@@ -126,7 +126,7 @@ TEST_CASE("Parse out-of-order compound arguments. Second variation" *
   program.add_argument("-c")
     .nargs(2)
     .default_value(std::vector<float>{0.0f, 0.0f})
-    .action([](const std::string& value) { return std::stof(value); });
+    .scan<'g', float>();
 
   program.parse_args({"./main", "-cb"}); 
 
diff --git a/test/test_invalid_arguments.cpp b/test/test_invalid_arguments.cpp
index a51be95..9750a39 100644
--- a/test/test_invalid_arguments.cpp
+++ b/test/test_invalid_arguments.cpp
@@ -33,7 +33,7 @@ TEST_CASE("Parse unknown optional argument" *
 
   bfm.add_argument("-m", "--mem")
     .default_value(64ULL)
-    .action([](const std::string& val) { return std::stoull(val); })
+    .scan<'u', unsigned long long>()
     .help("memory in MB to give the VMM when loading");
 
   REQUIRE_THROWS(bfm.parse_args({ "./test.exe", "-om" }));
diff --git a/test/test_issue_37.cpp b/test/test_issue_37.cpp
index 1ac3b7f..caa80a4 100644
--- a/test/test_issue_37.cpp
+++ b/test/test_issue_37.cpp
@@ -31,7 +31,7 @@ TEST_CASE("Issues with implicit values #37" * test_suite("implicit_values")) {
   m_bfm.add_argument("-m", "--mem")
     .default_value(100)
     .required()
-    .action([](const std::string &val) { return std::stoull(val); })
+    .scan<'u', unsigned long long>()
     .help("memory in MB to give the VMM when loading");
   m_bfm.parse_args({ "test", "-l", "blah", "-d", "-u" });
 
diff --git a/test/test_negative_numbers.cpp b/test/test_negative_numbers.cpp
index 4bac6ec..0e8ddb0 100644
--- a/test/test_negative_numbers.cpp
+++ b/test/test_negative_numbers.cpp
@@ -12,7 +12,7 @@ TEST_CASE("Parse negative integer" * test_suite("positional_arguments")) {
 
   program.add_argument("number")
     .help("Input number")
-    .action([](const std::string& value) { return std::stoi(value); });
+    .scan<'i', int>();
 
   program.parse_args({"./main", "-1"});
   REQUIRE(program.get<int>("number") == -1);
@@ -29,7 +29,7 @@ TEST_CASE("Parse negative integers into a vector" *
   program.add_argument("number")
     .help("Input number")
     .nargs(3)
-    .action([](const std::string& value) { return std::stoi(value); });
+    .scan<'i', int>();
 
   program.parse_args({"./main", "-1", "-2", "3"});
   REQUIRE(program["number"] == std::vector<int>{-1, -2, 3});
@@ -44,7 +44,7 @@ TEST_CASE("Parse negative float" * test_suite("positional_arguments")) {
 
   program.add_argument("number")
     .help("Input number")
-    .action([](const std::string& value) { return std::stof(value); });
+    .scan<'g', float>();
 
   program.parse_args({"./main", "-1.0"});
   REQUIRE(program.get<float>("number") == -1.0);
@@ -61,7 +61,7 @@ TEST_CASE("Parse negative floats into a vector" *
   program.add_argument("number")
     .help("Input number")
     .nargs(3)
-    .action([](const std::string& value) { return std::stod(value); });
+    .scan<'g', double>();
 
   program.parse_args({"./main", "-1.001", "-2.002", "3.003"});
   REQUIRE(program["number"] == std::vector<double>{-1.001, -2.002, 3.003});
@@ -76,7 +76,7 @@ TEST_CASE("Parse numbers in E notation" * test_suite("positional_arguments")) {
 
   program.add_argument("number")
     .help("Input number")
-    .action([](const std::string& value) { return std::stod(value); });
+    .scan<'g', double>();
 
   program.parse_args({"./main", "-1.2e3"});
   REQUIRE(program.get<double>("number") == -1200.0);
@@ -92,7 +92,7 @@ TEST_CASE("Parse numbers in E notation (capital E)" *
 
   program.add_argument("number")
     .help("Input number")
-    .action([](const std::string& value) { return std::stod(value); });
+    .scan<'g', double>();
 
   program.parse_args({"./main", "-1.32E4"});
   REQUIRE(program.get<double>("number") == -13200.0);
diff --git a/test/test_optional_arguments.cpp b/test/test_optional_arguments.cpp
index a31d5df..4d50254 100644
--- a/test/test_optional_arguments.cpp
+++ b/test/test_optional_arguments.cpp
@@ -85,8 +85,7 @@ TEST_CASE("Parse optional arguments of many values" *
           test_suite("optional_arguments")) {
   GIVEN("a program that accepts an optional argument of many values") {
     argparse::ArgumentParser program("test");
-    program.add_argument("-i").remaining().action(
-        [](const std::string &value) { return std::stoi(value); });
+    program.add_argument("-i").remaining().scan<'i', int>();
 
     WHEN("provided no argument") {
       THEN("the program accepts it but gets nothing") {
diff --git a/test/test_parent_parsers.cpp b/test/test_parent_parsers.cpp
index 2077265..301309f 100644
--- a/test/test_parent_parsers.cpp
+++ b/test/test_parent_parsers.cpp
@@ -21,7 +21,7 @@ TEST_CASE("Add parent to multiple parent parsers" *
   argparse::ArgumentParser parent_parser("main");
   parent_parser.add_argument("--parent")
     .default_value(0)
-    .action([](const std::string& value) { return std::stoi(value); });
+    .scan<'i', int>();
 
   argparse::ArgumentParser foo_parser("foo");
   foo_parser.add_argument("foo");
diff --git a/test/test_parse_args.cpp b/test/test_parse_args.cpp
index 6ca55a6..a3a0452 100644
--- a/test/test_parse_args.cpp
+++ b/test/test_parse_args.cpp
@@ -48,7 +48,7 @@ TEST_CASE("Parse a string argument without default value" *
 TEST_CASE("Parse an int argument with value" * test_suite("parse_args")) {
   argparse::ArgumentParser program("test");
   program.add_argument("--count")
-    .action([](const std::string& value) { return std::stoi(value); });
+    .scan<'i', int>();
   program.parse_args({ "test", "--count", "5" });
   REQUIRE(program.get<int>("--count") == 5);
 }
@@ -58,7 +58,7 @@ TEST_CASE("Parse an int argument with default value" *
   argparse::ArgumentParser program("test");
   program.add_argument("--count")
     .default_value(2)
-    .action([](const std::string& value) { return std::stoi(value); });
+    .scan<'i', int>();
   program.parse_args({ "test", "--count" });
   REQUIRE(program.get<int>("--count") == 2);
 }
@@ -66,7 +66,7 @@ TEST_CASE("Parse an int argument with default value" *
 TEST_CASE("Parse a float argument with value" * test_suite("parse_args")) {
   argparse::ArgumentParser program("test");
   program.add_argument("--ratio")
-    .action([](const std::string& value) { return std::stof(value); });
+    .scan<'g', float>();
   program.parse_args({ "test", "--ratio", "5.6645" });
   REQUIRE(program.get<float>("--ratio") == 5.6645f);
 }
@@ -76,7 +76,7 @@ TEST_CASE("Parse a float argument with default value" *
   argparse::ArgumentParser program("test");
   program.add_argument("--ratio")
     .default_value(3.14f)
-    .action([](const std::string& value) { return std::stof(value); });
+    .scan<'g', float>();
   program.parse_args({ "test", "--ratio" });
   REQUIRE(program.get<float>("--ratio") == 3.14f);
 }
@@ -84,7 +84,7 @@ TEST_CASE("Parse a float argument with default value" *
 TEST_CASE("Parse a double argument with value" * test_suite("parse_args")) {
   argparse::ArgumentParser program("test");
   program.add_argument("--ratio")
-    .action([](const std::string& value) { return std::stod(value); });
+    .scan<'g', double>();
   program.parse_args({ "test", "--ratio", "5.6645" });
   REQUIRE(program.get<double>("--ratio") == 5.6645);
 }
@@ -94,7 +94,7 @@ TEST_CASE("Parse a double argument with default value" *
   argparse::ArgumentParser program("test");
   program.add_argument("--ratio")
     .default_value(3.14)
-    .action([](const std::string& value) { return std::stod(value); });
+    .scan<'g', double>();
   program.parse_args({ "test", "--ratio" });
   REQUIRE(program.get<double>("--ratio") == 3.14);
 }
@@ -103,7 +103,7 @@ TEST_CASE("Parse a vector of integer arguments" * test_suite("parse_args")) {
   argparse::ArgumentParser program("test");
   program.add_argument("--vector")
     .nargs(5)
-    .action([](const std::string& value) { return std::stoi(value); });
+    .scan<'i', int>();
   program.parse_args({ "test", "--vector", "1", "2", "3", "4", "5" });
   auto vector = program.get<std::vector<int>>("--vector");
   REQUIRE(vector.size() == 5);
@@ -118,7 +118,7 @@ TEST_CASE("Parse a vector of float arguments" * test_suite("parse_args")) {
   argparse::ArgumentParser program("test");
   program.add_argument("--vector")
     .nargs(5)
-    .action([](const std::string& value) { return std::stof(value); });
+    .scan<'g', float>();
   program.parse_args({ "test", "--vector", "1.1", "2.2", "3.3", "4.4", "5.5" });
   auto vector = program.get<std::vector<float>>("--vector");
   REQUIRE(vector.size() == 5);
@@ -132,7 +132,7 @@ TEST_CASE("Parse a vector of float arguments" * test_suite("parse_args")) {
 TEST_CASE("Parse a vector of float without default value" *
           test_suite("parse_args")) {
   argparse::ArgumentParser program("test");
-  program.add_argument("--vector").scan<'f', float>().nargs(3);
+  program.add_argument("--vector").scan<'g', float>().nargs(3);
 
   WHEN("no value is provided") {
     program.parse_args({"test"});
@@ -164,7 +164,7 @@ TEST_CASE("Parse a vector of double arguments" * test_suite("parse_args")) {
   argparse::ArgumentParser program("test");
   program.add_argument("--vector")
     .nargs(5)
-    .action([](const std::string& value) { return std::stod(value); });
+    .scan<'g', double>();
   program.parse_args({ "test", "--vector", "1.1", "2.2", "3.3", "4.4", "5.5" });
   auto vector = program.get<std::vector<double>>("--vector");
   REQUIRE(vector.size() == 5);
@@ -178,8 +178,7 @@ TEST_CASE("Parse a vector of double arguments" * test_suite("parse_args")) {
 TEST_CASE("Parse a vector of string arguments" * test_suite("parse_args")) {
   argparse::ArgumentParser program("test");
   program.add_argument("--vector")
-    .nargs(5)
-    .action([](const std::string& value) { return value; });
+    .nargs(5);
   program.parse_args({ "test", "--vector", "abc", "def", "ghi", "jkl", "mno" });
   auto vector = program.get<std::vector<std::string>>("--vector");
   REQUIRE(vector.size() == 5);
diff --git a/test/test_positional_arguments.cpp b/test/test_positional_arguments.cpp
index 3b2b85c..f0d936c 100644
--- a/test/test_positional_arguments.cpp
+++ b/test/test_positional_arguments.cpp
@@ -32,7 +32,7 @@ TEST_CASE("Parse positional arguments with optional arguments" *
   program.add_argument("input");
   program.add_argument("output").nargs(2);
   program.add_argument("--num_iterations")
-    .action([](const std::string& value) { return std::stoi(value); });
+    .scan<'i', int>();
   program.parse_args({ "test", "rocket.mesh", "--num_iterations", "15", "thrust_profile.csv", "output.mesh" });
   REQUIRE(program.get<int>("--num_iterations") == 15);
   REQUIRE(program.get("input") == "rocket.mesh");
@@ -48,7 +48,7 @@ TEST_CASE("Parse positional arguments with optional arguments in the middle" *
   program.add_argument("input");
   program.add_argument("output").nargs(2);
   program.add_argument("--num_iterations")
-    .action([](const std::string& value) { return std::stoi(value); });
+    .scan<'i', int>();
   REQUIRE_THROWS(program.parse_args({ "test", "rocket.mesh", "thrust_profile.csv", "--num_iterations", "15", "output.mesh" }));
 }