inspect.lua

This function transform any Lua table into a human-readable representation of that table.

The objective here is human understanding (i.e. for debugging), not serialization or compactness.

Examples of use

"Array-like" tables are rendered horizontally:

inspect({1,2,3,4}) == "{ 1, 2, 3, 4 }"

"dictionary-like" tables are rendered with one element per line:

inspect({a=1,b=2}) == [[{
  a = 1,
  b = 2
}]]

The keys will be sorted alphanumerically when possible.

"Hybrid" tables will have the array part on the first line, and the dictionary part just below them:

inspect({1,2,3,b=2,a=1}) == [[{ 1, 2, 3,
  a = 1,
  b = 2
}]]

Tables can be nested, and will be indented with two spaces per level.

inspect({a={b=2}}) == [[{
  a = {
    b = 2
  }
}]]

inspect's second parameter allows controlling the maximum depth that will be printed out. When the max depth is reached, it'll just return {...}:

local t5 = {a = {b = {c = {d = {e = 5}}}}}

inspect(t5, 4) == [[{
  a = {
    b = {
      c = {
        d = {...}
      }
    }
  }
}]]

inspect(t5, 2) == [[{
  a = {
    b = {...}
  }
}]])

Functions, userdata and threads are simply rendered as <function x>, <userdata x> and <thread x> respectively:

inspect({ f = print, ud = some_user_data, thread = a_thread} ) == [[{
  f = <function 1>,
  u = <userdata 1>,
  thread = <thread 1>
}]])

If the table has a metatable, inspect will include it at the end, in a special field called <metatable>:

inspect(setmetatable({a=1}, {b=2}) == [[{
  a = 1
  <metatable> = {
    b = 2
  }
}]])

inspect can handle tables with loops inside them. It will print <id> right before the table is printed out the first time, and replace the whole table with <table id> from then on, preventing infinite loops.

a = {1, 2}
b = {3, 4, a}
a[3] = b -- a references b, and b references a
inspect(a) = "<1>{ 1, 2, { 3, 4, <table 1> } }"

Notice that since both a appears more than once in the expression, it is prefixed by <1> and replaced by <table 1> every time it appears later on.

Gotchas / Warnings

This method is not appropiate for saving/restoring tables. It is ment to be used by the programmer mainly while debugging a program.

Installation

Just copy the inspect.lua file somewhere in your projects (maybe inside a /lib/ folder) and require it accordingly.

Remember to store the value returned by require somewhere! (I suggest a local variable named inspect, altough others might like table.inspect)

local inspect = require 'inspect'
      -- or --
table.inspect = require 'inspect'

Also, make sure to read the license file; the text of that license file must appear somewhere in your projects' files.

Specs

This project uses busted for its specs. If you want to run the specs, you will have to install telescope first. Then just execute the following from the root inspect folder:

busted