local pp = require'pp'

Fast, compact serialization producing portable Lua source code.

TIP: If you’re on latest LuaJIT and you don’t need human-readable or diff’able output, use the built-in string.buffer:encode()1.

Input

• all Lua types except coroutines, userdata, cdata and C functions.
• the ffi int64_t and uint64_t types.
• values featuring __tostring or __pwrite metamethods (eg. tuples).

Output

• compact: no spaces, dot notation for identifier keys, minimal quoting of strings, implicit keys for the array part of tables.
• portable between LuaJIT 2, Lua 5.1, Lua 5.2: dot key notation only for ascii identifiers, numbers are in decimal, NaN and ±Inf are written as 0/0, 1/0 and -1/0 respectively.
• portable between Windows, Linux, Mac: quoting of \n and \r protects binary integrity when opening in text mode.
• embeddable: can be copy-pasted into Lua source code: quoting of \0 and \t and all other control characters protects binary integrity with code editors.
• human readable: indentation (optional, configurable); array part printed separately with implicit keys.
• stream-based: the string bits are written with a writer function to minimize the amount of string concatenation and memory footprint.
• deterministic: table keys are sorted by default, so that the output is usable with diff and checksum.
• non-identical: object identity is not tracked and is not preserved (table references are dereferenced).

Limitations

• object identity is not preserved.
• recursive: table nesting depth is stack-bound.
• some fractions are not compact eg. the fraction 5/6 takes 19 bytes vs 8 bytes in its native double format.
• strings need escaping which could become noticeable with large strings featuring many newlines, tabs, zero bytes, apostrophes, backslashes or control characters.
• loading back the output with the Lua interpreter is not safe.

API

pp(v1, ...)

Print the arguments to standard output. Only tables are pretty-printed, everything else gets printed raw. Cycle detection, indentation and sorting of keys are enabled in this mode. Unserializable values get a comment in place. Functions are skipped entirely.

pp.write(write, v, options...)

Pretty-print a value using a supplied write function that takes a string. The options can be given in a table or as separate args:

• indent - enable indentation (default is ’, pass false to get compact output).
• quote - string quoting to use eg. '"' (default is “’”).
• line_term - line terminator to use (default is '\n').
• onerror - enable error handling eg. function(err_type, v, depth) error(err_type..': '..tostring(v)) end (default is to add a comment).
• sort_keys - sort keys to get deterministic output (default is true).
• filter - filter keys, values or key/value combinations: filter(v[, k]) -> true|false

Defaults result in diff’able human-readable output that is good for both serialization and for inspecting.

Example:

local function chunks(t)
   return coroutine.wrap(function()
      return pp.write(coroutine.yield, t)
   end)
end

for s in chunks(t) do
   socket:send(s)
end

pp.save(path, v, options...)

Pretty-print a value to a file, prepending the string 'return '.

pp.load(path) -> v

Load back a saved value.

pp.stream(f, v, options...)

Pretty-print a value to an opened file.

pp.format(v, options...) -> s

Pretty-print a value to a string.

Last updated: 21 months ago | Edit on GitHub