using type() function to see if current string exist as table

Question

Is it possible to see if a string is the same as the name of a table?

For example: I know that a table called 'os' exists, and I have a string "os". Is there then a way to do this:

x="os"
if type(x)=="table" then
    print("hurra, the string is a table")
end

Of course this example wont work like I want it to because

type(x)

will just return "string".

The reason why I want to do this, is just because I wanted to list all existing Lua tables, so I made this piece of code:

alphabetStart=97
alphabetEnd=122

function findAllTables(currString, length)

    if type(allTables)=="nil"   then
        allTables={}
    end

    if type(currString)=="table" then
        allTables[#allTables+1]=currString
    end

    if #currString < length then
        for i=alphabetStart, alphabetEnd do
            findAllTables(currString..string.char(i), length)
        end
    end
end

findAllTables("", 2)

for i in pairs(allTables) do
    print(i)
end

I wouldn't be surprised if there is an easier method to list all existing tables, I'm just doing this for fun in my progress of learning Lua.

score 19 · Accepted Answer · edited Dec 07 '19 at 18:36

19

If you want to iterate over all global variables, you can use a for loop to iterate over the special _G table which stores them:

for key, value in pairs(_G) do
    print(key, value)
end

key will hold the variable name. You can use type(value) to check if the variable is a table.

To answer your original question, you can get a global variable by name with _G[varName]. So type(_G["os"]) will give "table".

edited Dec 07 '19 at 18:36

iono

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answered Mar 09 '11 at 18:38

interjay

107,303
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awesome, thank you very much. Knew there had to be an easy way to do this :) – Michelrandahl Mar 09 '11 at 18:48

score 4 · Answer 2 · answered Mar 14 '11 at 03:43

interjay gave the best way to actually do it. If you're interested, though, info on your original question can be found in the lua manual. Basically, you want:

mystr = "os"

f = loadstring("return " .. mystr);

print(type(f()))

loadstring creates a function containing the code in the string. Running f() executes that function, which in this case just returns whatever was in the string mystr.

using type() function to see if current string exist as table

2 Answers2