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local cache_methods = {};
local cache_mt = { __index = cache_methods };
local function new(size)
assert(size > 0, "cache size must be greater than zero");
local data = {};
return setmetatable({ data = data, count = 0, size = size, head = nil, tail = nil }, cache_mt);
end
local function _remove(list, m)
if m.prev then
m.prev.next = m.next;
end
if m.next then
m.next.prev = m.prev;
end
if list.tail == m then
list.tail = m.prev;
end
if list.head == m then
list.head = m.next;
end
list.count = list.count - 1;
end
local function _insert(list, m)
if list.head then
list.head.prev = m;
end
m.prev, m.next = nil, list.head;
list.head = m;
if not list.tail then
list.tail = m;
end
list.count = list.count + 1;
end
function cache_methods:set(k, v)
local m = self.data[k];
if m then
-- Key already exists
if v ~= nil then
-- Bump to head of list
_remove(self, m);
_insert(self, m);
m.value = v;
else
-- Remove from list
_remove(self, m);
self.data[k] = nil;
end
return;
end
-- New key
if v == nil then
return;
end
-- Check whether we need to remove oldest k/v
if self.count == self.size then
self.data[self.tail.key] = nil;
_remove(self, self.tail);
end
m = { key = k, value = v, prev = nil, next = nil };
self.data[k] = m;
_insert(self, m);
end
function cache_methods:get(k)
local m = self.data[k];
if m then
return m.value;
end
return nil;
end
function cache_methods:items()
local m = self.head;
return function ()
if not m then
return;
end
local k, v = m.key, m.value;
m = m.next;
return k, v;
end
end
return {
new = new;
}
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