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--!A cross-platform build utility based on Lua
--
-- Licensed under the Apache License, Version 2.0 (the "License");
-- you may not use this file except in compliance with the License.
-- You may obtain a copy of the License at
--
-- http://www.apache.org/licenses/LICENSE-2.0
--
-- Unless required by applicable law or agreed to in writing, software
-- distributed under the License is distributed on an "AS IS" BASIS,
-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-- See the License for the specific language governing permissions and
-- limitations under the License.
--
-- Copyright (C) 2015-present, Xmake Open Source Community.
--
-- @author ruki
-- @file singleton.lua
--
-- define module
local singleton = singleton or {}
-- get a singleton instance and create it if not exists
--
-- e.g.
--
-- function get_xxx()
-- return {xxx = 1}
-- end
-- local instance = singleton.get("key", get_xxx)
--
-- Or
--
-- function get_xxx()
--
-- -- get instance
-- local instance, inited = singleton.get(get_xxx)
-- if inited then
-- return instance
-- end
--
-- -- init instance
-- instance.xxx = 1
-- return instance
-- end
--
function singleton.get(key, init)
-- get key
key = tostring(key)
-- get all instances
local instances = singleton.instances()
-- get singleton instance
local inited = true
local instance = instances[key]
if instance == nil then
-- init instance
if init then
instance = init()
else
-- mark as not inited
inited = false
-- init instance
instance = {}
end
-- save this instance
instances[key] = instance
end
return instance, inited
end
-- get all singleton instances
function singleton.instances()
local instances = singleton._INSTANCES
if not instances then
instances = {}
singleton._INSTANCES = instances
end
return instances
end
-- return module: singleton
return singleton
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