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The function hashed below adds a metatable to the given table t, so that any write or read in the table will actually use a hash of the key instead of the key itself. This allows simulating the comparison of keys by values. To achieve that, make sure that two objects (table or userdata), with the same value will have the same hash.
local function gethash(k)
local hash = k
local mt = getmetatable(k)
local __hash = mt and mt.__hash
if type(__hash)=='function' then
hash = __hash(k)
elseif type(__hash)~='nil' then
hash = __hash
end
return hash
end
function hashed(t)
return setmetatable(t, {
__index = function(t, k)
return t[gethash(k)]
end,
__newindex = function(t, k, v)
rawset(t, gethash(k), v)
end,
})
end
local t1 = setmetatable({}, {__hash = 42})
local t2 = setmetatable({}, {__hash = 42})
local t = {}
t[t1] = "foo"
assert(t[t2]==nil)
t = hashed({})
t[t1] = "foo"
assert(t[t2]=="foo")
t[t2] = "bar"
assert(t[t1]=="bar")
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Edited September 2, 2008 6:15 pm GMT (diff)
