don't rely on shallow copy to construct new classes. also multiple ducks

data/scripts/types/list.lua

@@ -55,10 +55,11 @@ function List:__tostring()
   return s
 end
 
----Appends v to the end of the list.
----@param v any
-function List:push(v)
-  table.insert(self, v)
+---Appends value to the end of the list.
+---@param value any
+function List:push(value)
+  if self:has(value) then return end
+  table.insert(self, value)
 end
 
 ---Removes the last element in the list and returns it.
@@ -82,6 +83,13 @@ function List:filter(predicate)
   return filter(self, predicate)
 end
 
+---Removes the value at the given index.
+---@param idx integer
+---@return any
+function List:remove_at(idx)
+  return table.remove(self, idx)
+end
+
 ---Returns the index of value, if it exists in the list, -1 otherwise.
 ---@param value any
 ---@return integer
@@ -95,4 +103,27 @@ function List:find(value)
   end
   return idx
 end
+
+---Returns true if the value exists in the list.
+---@param value any
+---@return boolean
+function List:has(value)
+  return self:find(value) ~= -1
+end
+
+---Removes the value from the list, if it exists.
+---@param value any
+function List:remove_value(value)
+  local idx = self:find(value)
+  if idx ~= -1 then
+    table.remove(self, idx)
+  end
+end
+
+---Returns true if the list is empty.
+---@return boolean
+function List:is_empty()
+  return #self == 0
+end
+
 return List

data/scripts/types/signal.lua

@@ -1,10 +1,19 @@
 ---@class Signal
-local Signal = {
-  _connections = {}
-}
+---@field private _connections table
+local Signal = {}
 
 Signal.__index = Signal
 
+---Constructs a new signal.
+---@return Signal
+function Signal.new()
+  local s = {
+    _connections = {},
+  }
+  
+  return setmetatable(s, Signal)
+end
+
 ---Connects f to this signal. When the signal is emmitted, this function will be called.
 ---@param f function
 function Signal:connect(f)
@@ -26,14 +35,4 @@ function Signal:emit(...)
   end
 end
 
----Constructs a new signal.
----@return Signal
-function Signal.new()
-  local s = {
-    _connections = {},
-  }
-  
-  return setmetatable(s, Signal)
-end
-
 return Signal