string.dump()

The string.dump() function generates a binary string representing a precompiled version of a Lua function. This is useful for serializing or transmitting Lua functions, as well as for debugging purposes.

Syntax

string.dump(function, stripDebug)

Parameters

Return Value

The function returns:

• A binary string containing the precompiled representation of the Lua function.

Examples

Example 1: Dump a simple function

The function is dumped into its binary representation.

local function greet()
  return "Hello, world!"
end

local dumped = string.dump(greet)
print(dumped)

-- Output: A binary string representing the compiled function

Example 2: Serialize and reuse a function

Dump a function, save it to a file, and load it later.

local function square(x)
  return x * x
end

-- Serialize the function to a file
local dumped = string.dump(square)
local file = io.open("square_function.bin", "wb")
file:write(dumped)
file:close()

-- Later, load the function back
local file = io.open("square_function.bin", "rb")
local binary = file:read("*a")
file:close()

local loadedFunction = load(binary)
print(loadedFunction(5)) -- Output: 25

Example 3: Strip debug information

Use the stripDebug parameter to create a more compact binary representation.

local function sum(a, b)
  return a + b
end

local dumped = string.dump(sum, true) -- Strips debug information
print(dumped)

-- Output: A smaller binary string

Example 4: Error handling

string.dump() only works with Lua functions. Attempting to dump a non-function value will raise an error.

-- print(string.dump("not a function"))
-- Error: bad argument #1 to 'dump' (function expected, got string)

Use Cases

• Serialization: Save functions for reuse or transmission.
• Debugging: Analyze or compare the internal representation of Lua functions.
• Optimization: Strip debug information to reduce binary size for production use.

See also

• load(): Reconstructs a function from a binary string generated by string.dump().
• loadstring(): Similar to load(), but used for loading Lua code from strings (deprecated in Lua 5.2+).
• io.open(): Useful for saving or loading dumped functions from files.