seashell

A Luau module that produces a deterministic SHA-1 hash of a table's key structure.

Two tables that share identical keys — including nested table keys — always produce the same hash, regardless of their values.

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API

local Seashell = require(path.to.seashell)

-- Hash a plain string.
local digest: string = Seashell.hash_string("hello world")
-- → "2aae6c69..."

-- Get the canonical key-structure string of a table.
local sig: string = Seashell.signature_of({ name = "Ann", age = 30 })
-- → "age,name"

-- Hash a table's key structure.
local hash: string = Seashell.hash_table({
    name   = "Ann",
    age    = 30,
    address = {
        city = "New York",
        zip  = "10001",
    },
})
-- → SHA-1 of "address{city,zip},age,name"

Exported types

Type	Description
KeyType	string | number — the only accepted key types
HashResult	string — a 40-character lowercase hex SHA-1 digest
TableLike	{ [unknown]: unknown } — any table passed to the module

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Behaviour

Feature	Detail
Key ordering	Keys are sorted lexicographically (tostring) so the result is always deterministic
Nested tables	Represented as key{nested,keys} in the canonical string
Values ignored	Only keys (and whether a value is itself a table) affect the hash
Cyclic references	Detected and raised as an error before a stack overflow can occur
Invalid key types	Any key that is not a string or number raises an error
Hash algorithm	Pure-Luau SHA-1 via the bit32 library

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Serialisation format

Given the table

{
    name    = "Ann",
    age     = 30,
    address = { city = "New York", zip = "10001" },
}

the canonical string is:

address{city,zip},age,name

Keys at the same level are separated by ,; nested table keys are wrapped in {…}. This string is then SHA-1 hashed to produce the final digest.