Search code examples
lualua-tablemetatable

Print a table without metatables in Lua

Is it possible to print a table without using metatables in Lua?

In Roberto's book Programming in Lua, he mentions "The function print always calls tostring to format its output". However, if I override tostring in my table, then I get the following results:

> a = {}
> a.tostring = function() return "Lua is cool" end
> print(a)
table: 0x24038c0
Solution

  • It can NOT be done without metatables.

    The function print always calls tostring to format its output.

    You misunderstood this. Here, tostring is the function tostring, not a field of a table. So what it means is that print(t) will call print(tosstring(t)), that's it.

    For tables, tostring(t) will then find if it has a metamethod __tostring, and uses that as the result. So eventually, you still need a metatable.

    local t = {}
local mt = {__tostring = function() return "Hello Lua" end}
setmetatable(t, mt)
print(t)