Since sdbus-c++ knows types of D-Bus call/signal/property input/output parameters at compile time, why not assemble the D-Bus signature strings at compile time, too, instead of assembling them at run time as std::string with likely cost of (unnecessary) heap allocations...
std::array is well supported constexpr type in C++20, so we harness it to build the D-Bus signature string and store it into the binary at compile time.
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.
* feat: support serialization of array, span and unordered_map
* fix some spelling mistakes
* docs: update table of valid c++ types
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Co-authored-by: Marcel Hellwig <github@cookiesoft.de>
* Add missing nullptr check in Message::peekType().
* According to its specification, sd_bus_message_peek_type() sets a
given contents parameter to NULL if the next element in a message is
not a container. Since assigning a nullptr to a std::string has
undefined behaviour (typically resulting in an invalid memory access),
Message::peekType() must not assign contentsSig unconditionally.
