lua call function from a string with function name

Question

Is it possible in lua to execute a function from a string representing its name?
i.e: I have the string x = "foo", is it possible to do x() ?

If yes what is the syntax ?

Answer 1

To call a function in the global namespace (as mentioned by @THC4k) is easily done, and does not require loadstring().

x='foo' _G[x]() -- calls foo from the global namespace 

You would need to use loadstring() (or walk each table) if the function in another table, such as if x='math.sqrt'.

If loadstring() is used you would want to not only append parenthesis with ellipse (...) to allow for parameters, but also add return to the front.

x='math.sqrt' print(assert(loadstring('return '..x..'(...)'))(25)) --> 5 

or walk the tables:

function findfunction(x)   assert(type(x) == "string")   local f=_G   for v in x:gmatch("[^%.]+") do     if type(f) ~= "table" then        return nil, "looking for '"..v.."' expected table, not "..type(f)     end     f=f[v]   end   if type(f) == "function" then     return f   else     return nil, "expected function, not "..type(f)   end end  x='math.sqrt' print(assert(findfunction(x))(121)) -->11 

Answer 2

I frequently put a bunch of functions in a table:

functions = {        f1 = function(arg) print("function one: "..arg) end,        f2 = function(arg) print("function two: "..arg..arg) end,        ...,        fn = function(arg) print("function N: argh") end, } 

Then you can use a string as an table index and run your function like this

print(functions["f1"]("blabla")) print(functions["f2"]("blabla")) 

This is the result:

function one: blabla function two: blablablabla 

I find this to be cleaner than using loadstring(). If you don't want to create a special function table you can use _G['foo'].