1 --------------------------------------------------------------------------------
2 -- Serialize an object into a source code string. This string, when passed as
3 -- an argument to loadstring()(), returns an object structurally identical
4 -- to the original one. The following are currently supported:
5 -- * strings, numbers, booleans, nil
6 -- * functions without upvalues
7 -- * tables thereof. Tables cna have shared part, but can't be recursive yet.
8 -- Caveat: metatables and environments aren't saved.
9 --------------------------------------------------------------------------------
11 local no_identity = table.transpose { 'number', 'boolean', 'string', 'nil' }
13 function serialize (x)
15 local gensym_max = 0 -- index of the gensym() symbol generator
16 local seen_once = { } -- element->true set of elements seen exactly once in the table
17 local multiple = { } -- element->varname set of elements seen more than once
18 local nested = { } -- transient, set of elements currently being traversed
20 local function gensym()
21 gensym_max = gensym_max + 1 ; return "_" .. gensym_max
24 -----------------------------------------------------------------------------
25 -- First pass, list the tables and functions which appear more than once in x
26 -----------------------------------------------------------------------------
27 local function mark_multiple_occurences (x)
28 if no_identity [type(x)] then return end
29 if seen_once [x] then seen_once [x], multiple [x] = nil, gensym()
30 elseif multiple [x] then -- pass
31 elseif seen_once [x] = true end
33 if type (x) == 'table' then
35 for k, v in pairs (x) do
36 if nested [k] then error "Can't serialize recursive tables yet" end
37 mark_multiple_occurences (k)
38 mark_multiple_occurences (v)
44 local dumped = { } -- multiply occuring values already dumped in localdefs
45 local localdefs = { } -- already dumped local definitions as source code lines
47 -----------------------------------------------------------------------------
48 -- Second pass, dump the object; subparts occuring multiple times are dumped
49 -- in local variables which can be referenced multiple times;
50 -- care is taken to dump locla vars in asensible order.
51 -----------------------------------------------------------------------------
52 local function dump_val(x)
54 if x==nil then return 'nil'
55 elseif t=="number" then return tostring(x)
56 elseif t=="string" then return string.format("%q", x)
57 elseif t=="boolean" then return x and "true" or "false"
58 elseif t=="function" then
59 return string.format ("loadstring(%q,'@serialized')", string.dump (x))
60 elseif t=="table" then
62 for k, v in pairs(x) do
63 --------------------------------------------------------------------
64 -- if x occurs multiple times, dump the local var rather than the
65 -- value. If it's the first time it's dumped, also dump the content
67 --------------------------------------------------------------------
68 local function check_multiple (x)
69 local var = multiple [x]
70 if not var then return dump_val (x) end -- Occuring only once
71 if dumped [var] then return var end -- multiple occ, but already dumped
72 table.insert (localdefs, "local " .. var .. " = " .. dump_val (x)) -- dump
76 table.insert (acc, "[" .. check_multiple(k) .. "] = " .. check_multiple(v))
78 return "{ "..table.concat(acc,"; ").." }"
80 error ("Can't serialize data of type "..t)
84 mark_multiple_occurences (x)
85 local toplevel = dump_val (x)
86 return next (localdefs) and table.concat (localdefs, "\n") .. "\nreturn " .. toplevel
87 or "return "..toplevel