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40 lines
1.4 KiB
Lua
40 lines
1.4 KiB
Lua
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-- 4. Supporting recursive structures.
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--
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-- The issue here is that the following code will call itself
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-- indefinitely and ultimately cause a stack overflow:
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--
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-- local my_t = {}
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-- my_t.a = my_t
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-- local t_copy = copy2(my_t)
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--
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-- This happens to both copy1 and copy2, which each try to make
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-- a copy of my_t.a, which involves making a copy of my_t.a.a,
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-- which involves making a copy of my_t.a.a.a, etc. The
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-- recursive table my_t is perfectly legal, and it's possible to
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-- make a deep_copy function that can handle this by tracking
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-- which tables it has already started to copy.
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--
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-- Thanks to @mnemnion for pointing out that we should not call
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-- setmetatable() until we're doing copying values; otherwise we
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-- may accidentally trigger a custom __index() or __newindex()!
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--- Deep clones a given table.
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-- @source https://gist.github.com/tylerneylon/81333721109155b2d244
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-- @param obj table The table to clone.
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-- @returns table A deep copy of the given table.
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local function deepcopy(obj, seen)
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-- Handle non-tables and previously-seen tables.
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if type(obj) ~= 'table' then return obj end
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if seen and seen[obj] then return seen[obj] end
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-- New table; mark it as seen and copy recursively.
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local s = seen or {}
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local res = {}
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s[obj] = res
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for k, v in pairs(obj) do res[deepcopy(k, s)] = deepcopy(v, s) end
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return setmetatable(res, getmetatable(obj))
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end
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return deepcopy
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