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Set_mt = {}
function Set(t)
local set = {}
for k, l in ipairs(t) do
set[l] = true
end
setmetatable(set, Set_mt)
return set
end
function Set_mt.union(a, b)
local res = Set{}
for k in pairs(a) do res[k] = true end
for k in pairs(b) do res[k] = true end
return res
end
function Set_mt.intersection(a, b)
local res = Set{}
for k in pairs(a) do
res[k] = b[k]
end
return res
end
local function get_cache(a)
if not rawget(a, "__cache") then
rawset(a, "__cache", Set_mt.totable(a))
end
return rawget(a, "__cache")
end
function Set_mt.len(a)
return #get_cache(a)
end
function Set_mt.implode(a, sep)
return table.concat(get_cache(a), sep)
end
function Set_mt.totable(a)
local res = {}
for k in pairs(a) do
table.insert(res, k)
end
return res
end
function Set_mt.difference(a, b)
if getmetatable(b) ~= Set_mt then
if type(b) ~= "table" then
error(type(b).." is not a Set or table")
end
b=Set(b)
end
local res = Set{}
for k in pairs(a) do
res[k] = not b[k] or nil
end
rawset(res, "__cache", nil)
return res
end
function Set_mt.__index(a, i)
if type(i) == "number" then
return get_cache(a)[i]
end
return Set_mt[i] or rawget(a, i)
end
Set_mt.__add = Set_mt.union
Set_mt.__mul = Set_mt.intersection
Set_mt.__sub = Set_mt.difference
Set_mt.__len = Set_mt.len
Set_mt.__concat = Set_mt.implode
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