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--------------------------------------------------------------------------------

-- Serialize an object into a source code string. This string, when passed as

-- an argument to loadstring()(), returns an object structurally identical

-- to the original one. The following are currently supported:

-- * strings, numbers, booleans, nil

-- * functions without upvalues

-- * tables thereof. Tables can have shared part, but can't be recursive yet.

-- Caveat: metatables and environments aren't saved.

--------------------------------------------------------------------------------

local no_identity = { number=1, boolean=1, string=1, ['nil']=1 }

function serialize (x)

local gensym_max = 0 -- index of the gensym() symbol generator

local seen_once = { } -- element->true set of elements seen exactly once in the table

local multiple = { } -- element->varname set of elements seen more than once

local nested = { } -- transient, set of elements currently being traversed

local nest_points = { }

local nest_patches = { }

local function gensym()

gensym_max = gensym_max + 1 ; return gensym_max

end

-----------------------------------------------------------------------------

-- nest_points are places where a table appears within itself, directly or not.

-- for instance, all of these chunks create nest points in table x:

-- "x = { }; x[x] = 1", "x = { }; x[1] = x", "x = { }; x[1] = { y = { x } }".

-- To handle those, two tables are created by mark_nest_point:

-- * nest_points [parent] associates all keys and values in table parent which

-- create a nest_point with boolean `true'

-- * nest_patches contain a list of { parent, key, value } tuples creating

-- a nest point. They're all dumped after all the other table operations

-- have been performed.

--

-- mark_nest_point (p, k, v) fills tables nest_points and nest_patches with

-- informations required to remember that key/value (k,v) create a nest point

-- in table parent. It also marks `parent' as occuring multiple times, since

-- several references to it will be required in order to patch the nest

-- points.

-----------------------------------------------------------------------------

local function mark_nest_point (parent, k, v)

local nk, nv = nested[k], nested[v]

assert (not nk or seen_once[k] or multiple[k])

assert (not nv or seen_once[v] or multiple[v])

local mode = (nk and nv and "kv") or (nk and "k") or ("v")

local parent_np = nest_points [parent]

local pair = { k, v }

if not parent_np then parent_np = { }; nest_points [parent] = parent_np end

parent_np [k], parent_np [v] = nk, nv

table.insert (nest_patches, { parent, k, v })

seen_once [parent], multiple [parent] = nil, true

end

-----------------------------------------------------------------------------

-- First pass, list the tables and functions which appear more than once in x

-----------------------------------------------------------------------------

local function mark_multiple_occurences (x)

if no_identity [type(x)] then return end

if seen_once [x] then seen_once [x], multiple [x] = nil, true

elseif multiple [x] then -- pass

else seen_once [x] = true end

if type (x) == 'table' then

nested [x] = true

for k, v in pairs (x) do

if nested[k] or nested[v] then mark_nest_point (x, k, v) else

mark_multiple_occurences (k)

mark_multiple_occurences (v)

end

end

nested [x] = nil

end

end

local dumped = { } -- multiply occuring values already dumped in localdefs

local localdefs = { } -- already dumped local definitions as source code lines

-- mutually recursive functions:

local dump_val, dump_or_ref_val

--------------------------------------------------------------------

-- if x occurs multiple times, dump the local var rather than the

-- value. If it's the first time it's dumped, also dump the content

-- in localdefs.

--------------------------------------------------------------------

function dump_or_ref_val (x)

if nested[x] then return 'false' end -- placeholder for recursive reference

if not multiple[x] then return dump_val (x) end

local var = dumped [x]

if var then return "_[" .. var .. "]" end -- already referenced

local val = dump_val(x) -- first occurence, create and register reference

var = gensym()

table.insert(localdefs, "_["..var.."]="..val)

dumped [x] = var

return "_[" .. var .. "]"

end

-----------------------------------------------------------------------------

-- Second pass, dump the object; subparts occuring multiple times are dumped

-- in local variables which can be referenced multiple times;

-- care is taken to dump locla vars in asensible order.

-----------------------------------------------------------------------------

function dump_val(x)

local t = type(x)

if x==nil then return 'nil'

elseif t=="number" then return tostring(x)

elseif t=="string" then return string.format("%q", x)

elseif t=="boolean" then return x and "true" or "false"

elseif t=="function" then

return string.format ("loadstring(%q,'@serialized')", string.dump (x))

elseif t=="table" then

local acc = { }

local idx_dumped = { }

local np = nest_points [x]

for i, v in ipairs(x) do

if np and np[v] then

table.insert (acc, 'false') -- placeholder

else

table.insert (acc, dump_or_ref_val(v))

end

idx_dumped[i] = true

end

for k, v in pairs(x) do

if np and (np[k] or np[v]) then

--check_multiple(k); check_multiple(v) -- force dumps in localdefs

elseif not idx_dumped[k] then

table.insert (acc, "[" .. dump_or_ref_val(k) .. "] = " .. dump_or_ref_val(v))

end

end

return "{ "..table.concat(acc,", ").." }"

else

error ("Can't serialize data of type "..t)

end

end

local function dump_nest_patches()

for _, entry in ipairs(nest_patches) do

local p, k, v = unpack (entry)

assert (multiple[p])

local set = dump_or_ref_val (p) .. "[" .. dump_or_ref_val (k) .. "] = " ..

dump_or_ref_val (v) .. " -- rec "

table.insert (localdefs, set)

end

end

mark_multiple_occurences (x)

local toplevel = dump_or_ref_val (x)

dump_nest_patches()

if next (localdefs) then

return "local _={ }\n" ..

table.concat (localdefs, "\n") ..

"\nreturn " .. toplevel

else

return "return " .. toplevel

end

end