Support obtaining values from environment variables (#2)

Author: fantasy-peak

example/config.yaml

@@ -17,3 +17,4 @@ set_vec: [9, 5, 7]
 account_type: "Personal"
 v1: [8, 5, 65]
 default_opt: "yyds"
+ips: []

example/main.cpp

@@ -174,8 +174,9 @@ struct Config {
 	DefaultTest default_test;
 	std::string default_str{"hello default"};
 	std::optional<std::string> default_opt{std::nullopt};
+	std::vector<std::string> ips;
 };
-YCS_ADD_STRUCT(Config, ch, price, count, content, map, account_info, vec, set_vec, account_type, v1, default_test, default_str, default_opt)
+YCS_ADD_STRUCT(Config, ch, price, count, content, map, account_info, vec, set_vec, account_type, v1, default_test, default_str, default_opt, ips)
 
 std::string to_string(const Config& cfg) {
 	std::stringstream ss;
@@ -201,7 +202,13 @@ int main(int, char** argv) {
 	}
 #else
 	spdlog::info("Load yaml config");
-	auto [cfg, error] = yaml_cpp_struct::from_yaml<Config>(argv[1]);
+	// auto [cfg, error] = yaml_cpp_struct::from_yaml<Config>(argv[1]);
+	// if (!cfg) {
+	// 	spdlog::error("{}", error);
+	// 	return -1;
+	// }
+	//  export YCS_ENV_IPS=["Google","Runoob","Taobao"]
+	auto [cfg, error] = yaml_cpp_struct::from_yaml_env<Config>(argv[1], "YCS_ENV_");
 	if (!cfg) {
 		spdlog::error("{}", error);
 		return -1;

include/yaml_cpp_struct.hpp

@@ -143,6 +143,22 @@ inline std::tuple<std::optional<T>, std::string> from_yaml(const std::string& st
 	}
 }
 
+template <typename T>
+inline std::tuple<std::optional<T>, std::string> from_yaml_env(const std::string& str, const std::string& prefix) {
+	YAML::Node yaml_node = YAML::LoadFile(str);
+	for (YAML::iterator it = yaml_node.begin(); it != yaml_node.end(); ++it) {
+		std::string node_name = it->first.as<std::string>();
+		std::transform(node_name.begin(), node_name.end(), node_name.begin(), ::toupper);
+		auto environment_name = prefix + node_name;
+		auto environment_content_ptr = std::getenv(environment_name.data());
+		if (!environment_content_ptr)
+			continue;
+		std::string value{environment_content_ptr};
+		it->second = YAML::Load(value);
+	}
+	return from_yaml<T, false>(YAML::Dump(yaml_node));
+}
+
 } // namespace yaml_cpp_struct
 
 namespace YAML {