refactor: add strong types to public API (#414)

This introduces strong types for `std::string`-based D-Bus types. This facilitates safer, less error-prone and more expressive API.

What previously was `auto proxy = createProxy("org.sdbuscpp.concatenator", "/org/sdbuscpp/concatenator");` is now written like `auto proxy = createProxy(ServiceName{"org.sdbuscpp.concatenator"}, ObjectPath{"/org/sdbuscpp/concatenator"});`.

These types are:
  * `ObjectPath` type for the object path (the type has been around already but now is also used consistently in sdbus-c++ API for object path strings),
  * `InterfaceName` type for D-Bus interface names,
  * `BusName` (and its aliases `ServiceName` and `ConnectionName`) type for bus/service/connection names,
  * `MemberName` (and its aliases `MethodName`, `SignalName` and `PropertyName`) type for D-Bus method, signal and property names,
  * `Signature` type for the D-Bus signature (the type has been around already but now is also used consistently in sdbus-c++ API for signature strings),
  * `Error::Name` type for D-Bus error names.

tests/perftests/client.cpp

@@ -43,7 +43,7 @@ uint64_t totalDuration = 0;
 class PerftestProxy final : public sdbus::ProxyInterfaces<org::sdbuscpp::perftests_proxy>
 {
 public:
-    PerftestProxy(std::string destination, std::string objectPath)
+    PerftestProxy(sdbus::ServiceName destination, sdbus::ObjectPath objectPath)
         : ProxyInterfaces(std::move(destination), std::move(objectPath))
     {
         registerProxy();
@@ -101,9 +101,9 @@ std::string createRandomString(size_t length)
 //-----------------------------------------
 int main(int /*argc*/, char */*argv*/[])
 {
-    const char* destinationName = "org.sdbuscpp.perftests";
-    const char* objectPath = "/org/sdbuscpp/perftests";
-    PerftestProxy client(destinationName, objectPath);
+    sdbus::ServiceName destination{"org.sdbuscpp.perftests"};
+    sdbus::ObjectPath objectPath{"/org/sdbuscpp/perftests"};
+    PerftestProxy client(std::move(destination), std::move(objectPath));
 
     const unsigned int repetitions{20};
     unsigned int msgCount = 1000;

tests/perftests/perftests-adaptor.h

@@ -16,7 +16,7 @@ namespace sdbuscpp {
 class perftests_adaptor
 {
 public:
-    static constexpr const char* INTERFACE_NAME = "org.sdbuscpp.perftests";
+    static inline const sdbus::InterfaceName INTERFACE_NAME{"org.sdbuscpp.perftests"};
 
 protected:
     perftests_adaptor(sdbus::IObject& object)

tests/perftests/perftests-proxy.h

@@ -16,7 +16,7 @@ namespace sdbuscpp {
 class perftests_proxy
 {
 public:
-    static constexpr const char* INTERFACE_NAME = "org.sdbuscpp.perftests";
+    static inline const sdbus::InterfaceName INTERFACE_NAME{"org.sdbuscpp.perftests"};
 
 protected:
     perftests_proxy(sdbus::IProxy& proxy)

tests/perftests/server.cpp

@@ -40,7 +40,7 @@ std::string createRandomString(size_t length);
 class PerftestAdaptor final : public sdbus::AdaptorInterfaces<org::sdbuscpp::perftests_adaptor>
 {
 public:
-    PerftestAdaptor(sdbus::IConnection& connection, std::string objectPath)
+    PerftestAdaptor(sdbus::IConnection& connection, sdbus::ObjectPath objectPath)
         : AdaptorInterfaces(connection, std::move(objectPath))
     {
         registerAdaptor();
@@ -92,11 +92,11 @@ std::string createRandomString(size_t length)
 //-----------------------------------------
 int main(int /*argc*/, char */*argv*/[])
 {
-    const char* serviceName = "org.sdbuscpp.perftests";
+    sdbus::ServiceName serviceName{"org.sdbuscpp.perftests"};
     auto connection = sdbus::createSystemBusConnection(serviceName);
 
-    const char* objectPath = "/org/sdbuscpp/perftests";
-    PerftestAdaptor server(*connection, objectPath);
+    sdbus::ObjectPath objectPath{"/org/sdbuscpp/perftests"};
+    PerftestAdaptor server(*connection, std::move(objectPath));
 
     connection->enterEventLoop();
 }