AP_Scripting: Parameter helper: allow optional param name in constructior

libraries/AP_Scripting/AP_Scripting_helpers.cpp

@@ -1,7 +1,40 @@
 #include "AP_Scripting_helpers.h"
+#include <AP_Scripting/lua_generated_bindings.h>
 
 /// Fast param access via pointer helper class
 
+// Custom lua constructor with optional param name
+int lua_new_Parameter(lua_State *L) {
+
+    const int args = lua_gettop(L);
+    if (args > 1) {
+        return luaL_argerror(L, args, "too many arguments");
+    }
+    const char * name = nullptr;
+    if (args == 1) {
+        name = luaL_checkstring(L, 1);
+    }
+
+    // This chunk is the same as the auto generated constructor
+    luaL_checkstack(L, 2, "Out of stack");
+    void *ud = lua_newuserdata(L, sizeof(Parameter));
+    memset(ud, 0, sizeof(Parameter));
+    new (ud) Parameter();
+    luaL_getmetatable(L, "Parameter");
+    lua_setmetatable(L, -2);
+
+    if (args == 0) {
+        // no arguments, nothing to do
+        return 1;
+    }
+
+    if (!static_cast<Parameter*>(ud)->init(name)) {
+        return luaL_error(L, "No parameter: %s", name);
+    }
+
+    return 1;
+}
+
 // init by name
 bool Parameter::init(const char *name)
 {

libraries/AP_Scripting/AP_Scripting_helpers.h

@@ -1,6 +1,9 @@
 #pragma once
 
 #include <AP_Param/AP_Param.h>
+#include "lua/src/lua.hpp"
+
+int lua_new_Parameter(lua_State *L);
 
 /// Fast param access via pointer helper
 class Parameter

libraries/AP_Scripting/docs/docs.lua

@@ -296,7 +296,8 @@ function mavlink_mission_item_int_t_ud:param1(value) end
 local Parameter_ud = {}
 
 ---@return Parameter_ud
-function Parameter() end
+---@param name? string
+function Parameter(name) end
 
 -- desc
 ---@param value number

libraries/AP_Scripting/examples/param_get_set_test.lua

@@ -14,6 +14,20 @@ if not fake_param:init('FAKE_PARAM') then
   gcs:send_text(6, 'get FAKE_PARAM failed')
 end
 
+-- Can also pass param string in constructor to remove the need to init manualy
+local user_param = Parameter('SCR_USER1')
+-- this will error out for a bad parameter
+-- Parameter('FAKE_PARAM')
+local success, err = pcall(Parameter,'FAKE_PARAM')
+gcs:send_text(0, "Lua Caught Error: " .. err)
+-- this allows this example to catch the otherwise fatal error
+-- not recommend if error is possible/expected, use separate construction and init
+
+-- local user_param = Parameter('SCR_USER1')
+-- is equivalent to:
+-- local user_param = Parameter()
+-- assert(user_param:init('SCR_USER1'), 'No parameter: SCR_USER1')
+
 function update() -- this is the loop which periodically runs
 
   -- get and print all the scripting parameters
@@ -64,6 +78,12 @@ function update() -- this is the loop which periodically runs
     gcs:send_text(6, 'LUA: read SCR_VM_I_COUNT failed')
   end
 
+  local user = user_param:get()
+  if user then
+    gcs:send_text(6, string.format('LUA: SCR_USER1: %i', user))
+  else
+    gcs:send_text(6, 'LUA: read SCR_USER1 failed')
+  end
 
   count = count + 1;
 

libraries/AP_Scripting/generator/description/bindings.desc

@@ -326,6 +326,7 @@ singleton AP_Param method add_table boolean uint8_t 0 200 string uint8_t 1 63
 singleton AP_Param method add_param boolean uint8_t 0 200 uint8_t 1 63 string float'skip_check
 
 include AP_Scripting/AP_Scripting_helpers.h
+userdata Parameter creation lua_new_Parameter
 userdata Parameter method init boolean string
 userdata Parameter method init_by_info boolean uint16_t 0 UINT16_MAX uint32_t'skip_check ap_var_type'enum AP_PARAM_INT8 AP_PARAM_FLOAT
 userdata Parameter method get boolean float'Null