Only use native functions to obtain skill/experience

The former cache was actually slightly slower than calling the
corresponding functions directly

manipulator/gui/manipulator.lua

@@ -32,7 +32,6 @@ function manipulator:init(args)
     self.grid_idx = 1
     self.grid_rows = {}
     self.diff_enabled = storage.diff_enabled
-    skill_cache:clear()
     p_start('init units')
     for idx, u in pairs(self.units) do
         self.grid_rows[u] = penarray.new(#SKILL_COLUMNS, 1)
@@ -184,12 +183,12 @@ function manipulator:onRenderBody(p)
         end
         p:string(unit.status.labors[col.labor] and 'Enabled' or 'Not Enabled', {fg = COLOR_LIGHTBLUE})
     else
-        local skill = skill_cache:get(unit, col.skill)
-        local lvl = skill.rating
+        local lvl = skills.rating(unit, col.skill)
         local prof = df.job_skill.attrs[col.skill].caption_noun
         p:string((lvl > 0 and SKILL_LEVELS[lvl].name or 'Not') .. ' ' .. prof, {fg = COLOR_LIGHTBLUE})
         if lvl < #SKILL_LEVELS then
-            p:string(' '):string(('(%i/%i)'):format(skill.experience, SKILL_LEVELS[lvl > 0 and lvl or 1].points), {fg = COLOR_LIGHTBLUE})
+            p:string(' '):string(('(%i/%i)'):format(skills.experience(unit, col.skill),
+                SKILL_LEVELS[lvl > 0 and lvl or 1].points), {fg = COLOR_LIGHTBLUE})
         end
     end
     p:newline()
@@ -227,7 +226,7 @@ function manipulator:update_grid_tile(x, y)
     local skill = SKILL_COLUMNS[x].skill
     local labor = SKILL_COLUMNS[x].labor
     if skill ~= df.job_skill.NONE then
-        local level = skill_cache:get(unit, skill).rating
+        local level = skills.rating(unit, skill)
         c = level > 0 and SKILL_LEVELS[level].abbr or '-'
     end
     if labor ~= df.unit_labor.NONE then

manipulator/utils.lua

@@ -79,6 +79,20 @@ if dfhack.units.getKillCount == nil then
     end
 end
 
+skills = {}
+function skills.experience(unit, skill)
+    return dfhack.units.getExperience(unit._native, skill)
+end
+
+function skills.rating(unit, skill)
+    local rating = dfhack.units.getNominalSkill(unit._native, skill) + 1
+    local exp = skills.experience(unit, skill)
+    if exp == 0 and rating == 1 then
+        return 0
+    end
+    return rating
+end
+
 OutputString = dfhack.screen.paintString
 
 function OutputKeyString(pen, x, y, key, str)
@@ -199,23 +213,11 @@ function UnitAttrCache:clear()
     self.cache = {}
 end
 
-skill_cache = UnitAttrCache()
-function skill_cache:lookup(unit, skill)
-    local ret = {
-        rating = dfhack.units.getNominalSkill(unit._native, skill) + 1,
-        experience = dfhack.units.getExperience(unit._native, skill)
-    }
-    if ret.experience == 0 and ret.rating == 1 then
-        ret.rating = 0
-    end
-    return ret
-end
-
 sort = {
     skill = function(u1, u2, skill)
-        local level_diff = skill_cache:get(u2, skill).rating - skill_cache:get(u1, skill).rating
+        local level_diff = skills.rating(u2, skill) - skills.rating(u1, skill)
         if level_diff ~= 0 then return level_diff end
-        return skill_cache:get(u2, skill).experience - skill_cache:get(u1, skill).experience
+        return skills.experience(u2, skill) - skills.experience(u1, skill)
     end
 }