Added named systems

src/systems.lua

@@ -0,0 +1,29 @@
+-- Systems
+
+local PATH = (...):gsub('%.[^%.]+$', '')
+
+local Type = require(PATH..".type")
+
+local Systems = {}
+
+function Systems.register(name, system)
+    if (type(name) ~= "string") then
+        error("bad argument #1 to 'Systems.register' (string expected, got "..type(name)..")", 3)
+    end
+
+    if (not Type.isBaseSystem(system)) then
+        error("bad argument #2 to 'Systems.register' (baseSystem expected, got "..type(system)..")", 3)
+    end
+
+    if (rawget(Systems, name)) then
+        error("bad argument #2 to 'Systems.register' (System with name '"..name.."' is already registerd)", 3)
+    end
+
+    Systems[name] = system
+end
+
+return setmetatable(Systems, {
+    __index = function(_, name)
+        error("Attempt to index system '"..tostring(name).."' that does not exist / was not registered", 2)
+    end
+})