hmon: C++ interface logic monitor post-review fix

Post-review fixes do C++ interface of logic monitor.

Author: arkjedrz

src/health_monitoring_lib/cpp/include/score/hm/tag.h

@@ -25,30 +25,27 @@ template <typename T>
 class Tag
 {
   public:
-    /// Create an empty tag.
-    Tag() : data_{nullptr}, length_{0} {}
-
     /// Create a new tag from a C-style string.
     template <size_t N>
     explicit Tag(const char (&tag)[N]) : data_(tag), length_(N - 1)
     {
     }
 
-    bool operator==(const T& other)
+    bool operator==(const T& other) const noexcept
     {
         std::string_view this_sv{data_, length_};
         std::string_view other_sv{other.data_, other.length_};
         return this_sv.compare(other_sv) == 0;
     }
 
-    bool operator!=(const T& other)
+    bool operator!=(const T& other) const noexcept
     {
         return !(*this == other);
     }
 
   private:
     /// SAFETY: This has to be FFI compatible with the Rust side representation.
-    const char* const data_;
+    const char* data_;
     size_t length_;
 };
 

src/health_monitoring_lib/cpp/logic_monitor.cpp

@@ -81,7 +81,7 @@ score::cpp::expected<StateTag, Error> LogicMonitor::state()
     auto monitor_handle{monitor_handle_.as_rust_handle()};
     SCORE_LANGUAGE_FUTURECPP_PRECONDITION(monitor_handle.has_value());
 
-    StateTag state_tag;
+    StateTag state_tag{""};
     auto result{logic_monitor_state(monitor_handle.value(), &state_tag)};
     if (result != kSuccess)
     {

src/health_monitoring_lib/rust/logic/ffi.rs

@@ -77,10 +77,10 @@ pub extern "C" fn logic_monitor_builder_add_state(
     // `allowed_states` must contain a valid continuous array.
     // Number of elements must match `num_allowed_states`.
     // Null is allowed when `num_allowed_states` equals 0.
-    let allowed_states: Vec<StateTag> = if num_allowed_states > 0 {
-        unsafe { core::slice::from_raw_parts(allowed_states, num_allowed_states).to_vec() }
+    let allowed_states = if num_allowed_states > 0 {
+        unsafe { core::slice::from_raw_parts(allowed_states, num_allowed_states) }
     } else {
-        Vec::new()
+        &[]
     };
 
     // SAFETY:
@@ -90,7 +90,7 @@ pub extern "C" fn logic_monitor_builder_add_state(
     let mut logic_monitor_builder =
         FFIBorrowed::new(unsafe { Box::from_raw(logic_monitor_builder_handle as *mut LogicMonitorBuilder) });
 
-    logic_monitor_builder.add_state_internal(state, &allowed_states);
+    logic_monitor_builder.add_state_internal(state, allowed_states);
 
     FFICode::Success
 }