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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
local cache_methods = {};
local cache_mt = { __index = cache_methods };
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 true;
end
-- New key
if v == nil then
return true;
end
-- Check whether we need to remove oldest k/v
if self._count == self.size then
local tail = self._tail;
local on_evict, evicted_key, evicted_value = self._on_evict, tail.key, tail.value;
if on_evict ~= nil and (on_evict == false or on_evict(evicted_key, evicted_value) == false) then
-- Cache is full, and we're not allowed to evict
return false;
end
_remove(self, tail);
self._data[evicted_key] = nil;
end
m = { key = k, value = v, prev = nil, next = nil };
self._data[k] = m;
_insert(self, m);
return true;
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
function cache_methods:count()
return self._count;
end
function cache_methods:head()
local head = self._head;
if not head then return nil, nil; end
return head.key, head.value;
end
function cache_methods:tail()
local tail = self._tail;
if not tail then return nil, nil; end
return tail.key, tail.value;
end
local function new(size, on_evict)
size = assert(tonumber(size), "cache size must be a number");
size = math.floor(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, _on_evict = on_evict }, cache_mt);
end
return {
new = new;
}
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