Lua - Function Call as arguments

We can call functions and pass there responses as an argument in a lua function. As Lua function can return more than one value, we need to know the rules on how arguments are passed in multiple scenarios. We're using following functions in the examples discussed below:

-- returns 1 result
function func1 () 
   return 'a' 
end       

-- returns 2 results
function func2 () 
   return 'a','b' 
end   

Case: Calling function only as an argument

If a function is called as an only argument, all responses are used. See the example below−

main.lua

-- returns 1 result
function func1 ()
   return 'a'
end

-- returns 2 results
function func2 ()
   return 'a','b'
end

function printValues(...)
   print(...)
end


-- pass a function with one returned value
printValues(func1())   -- a

-- pass a function with two returned value
printValues(func2())   -- a   b

Output

When we run the above code, we will get the following output−

a
a   b

Case: Calling function as last argument along with other parameters

If a function call is the last argument then all responses are used. See the example below−

main.lua

-- returns 1 result
function func1 ()
   return 'a'
end

-- returns 2 results
function func2 ()
   return 'a','b'
end

function printValues(...)
   print(...)
end


-- pass a function with one returned value
printValues(1, 2, 3, func1())   -- 1   2   3   a

-- pass a function with two returned value
printValues(1, 2, 3, func2())   -- 1   2   3   a   b

Output

When we run the above code, we will get the following output−

1   2   3   a
1   2   3   a   b

Case: Calling function but not as last argument

If a function call is not the last argument, then only one response is used and other values are discarded. See the example below−

main.lua

-- returns 1 result
function func1 ()
   return 'a'
end

-- returns 2 results
function func2 ()
   return 'a','b'
end

function printValues(...)
   print(...)
end


-- pass a function with one returned value
printValues(1, func1(), 2, 3, )   -- 1  a  2  3

-- pass a function with two returned value
printValues(1, func2(), 2, 3, )   -- 1  a  2  3

Output

When we run the above code, we will get the following output−

1  a  2  3
1  a  2  3