[*] Style improvements, make constructors callable by :.

That is the recommended style for class constructors.

slider.lua

@@ -4,14 +4,16 @@
 -- @copyright 2022, The DoubleFourteen Code Forge
 -- @author Lorenzo Cogotti, Andrea Pasquini
 --
---- Slider widget receives the following callbacks: @{yui.Widget.WidgetCallbacks|onEnter}(), @{yui.Widget.WidgetCallbacks|onChange}(), @{yui.Widget.WidgetCallbacks|onLeave}().
+-- Slider widget receives the following callbacks: @{yui.Widget.WidgetCallbacks|onEnter}(), @{yui.Widget.WidgetCallbacks|onChange}(), @{yui.Widget.WidgetCallbacks|onLeave}().
 
 local BASE = (...):gsub('slider$', '')
 
 local Widget = require(BASE..'widget')
 local core = require(BASE..'core')
 
-local Slider = setmetatable({}, Widget)
+local Slider = setmetatable({
+    __call = function(cls, args) return cls:new(args) end
+}, Widget)
 Slider.__index = Slider
 
 --- Attributes accepted by the @{Slider} widget beyond the standard @{yui.Widget.WidgetAttributes|attributes}
@@ -21,15 +23,15 @@ Slider.__index = Slider
 -- @field max (number) max value of the slider
 -- @field vertical (boolean) true for vertical slider, false or nil for horizontal slider
 -- @field value (number) default value
--- @field step (number) number of slider's steps 
+-- @field step (number) number of slider's steps
 -- @field cornerRadius (number) radius for rounded corners
 -- @table SliderAttributes
 
 
 --- Slider constructor
 -- @param args (@{SliderAttributes}) widget attributes
-function Slider.new(args)
-    local self = setmetatable(args, Slider)
+function Slider:new(args)
+    self = setmetatable(args, self)
 
     self.color = self.color or core.theme.color
     self.cornerRadius = self.cornerRadius or core.theme.cornerRadius
@@ -41,7 +43,7 @@ function Slider.new(args)
     return self
 end
 
-function Slider:onPointerInput(px,py, clicked, down)
+function Slider:onPointerInput(px,py, _, down)
     self:grabFocus()
     if not down then
         return