Function params: use constraint to enforce length, template specialisation for default case

README.md

@@ -91,7 +91,12 @@ ThingSetUserFunction<0x410, 0x0, int, std::string &> xStringLength(getStringLeng
 ```
 
 Note that, by default, parameters' IDs will be generated by incrementing the function
-ID. It is possible to override this.
+ID. It is possible to override this. Parameter names will be generated from a combination of the
+function name, parameter type and parameter index. This too can be overridden:
+
+```c++
+ThingSetNamedUserFunction<0x470, 0x0, "xNamed", ThingSetParameterNames<"uAlpha", "uBeta">, int, uint16_t, float> xNamed([](uint16_t, float) { return 0; });
+```
 
 Once you have declared your properties and functions, instantiate a server with an appropriate
 transport to expose them to clients.

include/thingset++/ThingSetFunction.hpp

@@ -49,13 +49,27 @@ struct ThingSetParameterNames
 {
     static constexpr size_t count = sizeof...(Names);
 
-    template <size_t Index>
+    template <StringLiteral Name, size_t Index, typename ParameterType>
     static constexpr auto get()
     {
         return std::get<Index>(std::tuple{ Names... });
     }
 };
 
+/// @brief Empty specialisation of ThingSetParameterNames for the
+/// default case which auto-generates parameter names.
+template <>
+struct ThingSetParameterNames<>
+{
+    static constexpr size_t count = 0;
+
+    template <StringLiteral Name, size_t Index, typename ParameterType>
+    static constexpr auto get()
+    {
+        return Name + ThingSetType<std::remove_cvref_t<ParameterType>>::name + "_" + to_string_t<1 + Index>();
+    }
+};
+
 /// @brief Represents an executable function.
 /// @tparam Id The unique integer ID of the ThingSet node.
 /// @tparam ParentId The integer ID of the parent node.
@@ -66,11 +80,9 @@ struct ThingSetParameterNames
 /// @tparam Result The return type of the function.
 /// @tparam ...Args The argument types of the function, if any.
 template <uint16_t Id, uint16_t ParentId, StringLiteral Name, ThingSetAccess Access, uint16_t FirstArgumentId, typename ParamNames, typename Result, typename... Args>
+    requires (ParamNames::count == 0 || ParamNames::count == sizeof...(Args))
 class ThingSetFunction : public IdentifiableThingSetParentNode<Id, ParentId, Name>, public ThingSetInvocable
 {
-    static_assert(ParamNames::count == 0 || ParamNames::count == sizeof...(Args),
-                  "ThingSetParameterNames must either be empty or name every argument");
-
 private:
     template <uint16_t ChildId, StringLiteral ArgName, typename T>
     class ThingSetFunctionParameter : public IdentifiableThingSetNode<ChildId, Id, ArgName>
@@ -108,12 +120,7 @@ class ThingSetFunction : public IdentifiableThingSetParentNode<Id, ParentId, Nam
 
         static constexpr auto argName()
         {
-            if constexpr (ParamNames::count != 0) {
-                return ParamNames::template get<Index>();
-            }
-            else {
-                return Name + ThingSetType<std::remove_cvref_t<ParameterType>>::name + "_" + to_string_t<1 + Index>();
-            }
+            return ParamNames::template get<Name, Index, ParameterType>();
         }
 
         typedef ThingSetFunctionParameter<FirstArgumentId + 0 + Index, argName(), ParameterType> type;