add Widget:defineAttribute, fixes #16

luigi/widget.lua

@@ -53,7 +53,7 @@ end
 -- look for properties in attributes, Widget, style, and theme
 local function metaIndex (self, property)
     -- look in widget's own attributes
-    local A = Attribute[property]
+    local A = self.attributeDescriptors[property] or Attribute[property]
     if A then
         local value = A.get and A.get(self, property)
             or self.attributes[property]
@@ -76,7 +76,7 @@ end
 
 -- setting attributes triggers special behavior
 local function metaNewIndex (self, property, value)
-    local A = Attribute[property]
+    local A = self.attributeDescriptors[property] or Attribute[property]
     if A then
         if A.set then
             A.set(self, value, property)
@@ -121,6 +121,7 @@ local function metaCall (Widget, layout, self)
     self.position = { x = nil, y = nil }
     self.dimensions = { width = nil, height = nil }
     self.attributes = {}
+    self.attributeDescriptors = {}
 
     setmetatable(self, { __index = metaIndex, __newindex = metaNewIndex })
 
@@ -138,6 +139,26 @@ local function metaCall (Widget, layout, self)
     return self
 end
 
+--[[--
+Define a custom attribute for this widget.
+
+@tparam string name
+The name of the attribute.
+
+@tparam table descriptor
+A table, optionally containing `get` and `set` functions (see `Attribute`).
+
+@treturn Widget
+Return this widget for chaining.
+--]]--
+function Widget:defineAttribute (name, descriptor)
+    self.attributeDescriptors[name] = descriptor
+    local value = rawget(self, name)
+    rawset(self, name, nil)
+    self[name] = value
+    return self
+end
+
 --[[--
 Fire an event on this widget and each ancestor.
 

luigi/widget/radio.lua

@@ -15,22 +15,39 @@ standard themes, the widget's value should be indicated in some other way.
 @widget radio
 --]]--
 
--- TODO: make `group` a first-class attribute
 local groups = {}
 
-return function (self)
-    local groupName = self.group or 'default'
-
-    if not groups[groupName] then
-        groups[groupName] = {}
+local function remove (t, value)
+    for i, v in t do
+        if v == value then return table.remove(t, i) end
     end
+end
 
-    local group = groups[groupName]
-
+local function setGroup (self, value)
+    -- remove the widget from the old group
+    local oldValue = self.attributes.group
+    local oldGroup = oldValue and groups[oldValue]
+    if oldGroup then
+        remove(oldGroup, self)
+        if #oldGroup < 1 then
+            groups[oldValue] = nil
+        end
+    end
+    -- add the widget to the new group, or 'default' if no group specified
+    value = value or 'default'
+    if not groups[value] then
+        groups[value] = {}
+    end
+    local group = groups[value]
     group[#group + 1] = self
+    self.attributes.group = value
+end
+
+return function (self)
+    self:defineAttribute('group', { set = setGroup })
 
     self:onPress(function ()
-        for _, widget in ipairs(group) do
+        for _, widget in ipairs(groups[self.group]) do
             widget.value = widget == self
         end
     end)