metatable 操作 lua 13.1

metatable.lua

Set = {}

function Set.new(t)
	local set = {}
	setmetatable(set, Set.mt)
	for _, l in ipairs(t) do set[l] = true end
	return set
end

function Set.union(a, b)
	local res = Set.new{}
	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.intersection(a, b)
	local res = Set.new{}
	for k in pairs(a) do
		res[k] = b[k]
	end
	return res
end

function Set.tostring(set)
	local s= "{"
	local sep = ""
	for e in pairs(set) do
		s = s .. sep .. e
		sep = ","
	end
	return s .. "}"
end

function Set.print(s)
	print(Set.tostring(s))
end

Set.mt = {}

s1 = Set.new{10, 20, 30, 50}
s2 = Set.new{30, 1}
print(getmetatable(s1))
print(getmetatable(s2))

Set.mt.__add = Set.union

s3 = s1 + s2
Set.print(s3)

Set.mt.__mul = Set.intersection
Set.print((s1+s2)*s1)