Lua, Error Handling pcall()

Question

local a = {1,2,3,4}

print(pcall(#a[1])) -- still error

Should pcall() return false if error and true if all good?How do I handle errors?

Solution 1

-- Example 1. 

a = {1,2,3,4}

function check()
   return #a[1]
end

print(pcall(check)) -- false | attempt to get length of field '?' (a number value)

local v, massage = pcall(check)

print(v, massage) -- "v" contains false or true, "massage" contains error string

-- Example 2.
-- Passing function and parameter...

function f(v)
   return v + 2
end

a, b = pcall(f, 1)
print(a, b) --> true | 3

a, b = pcall(f, "a")
print(a, b) -- false | attempt to perform arithmetic on local 'v' (a string value)

For pcall() to work, function needs to be passed with out brackets.

Solution 2

The first passed in parameter in pcall is function name, what you have in the example is array, not legal I am afraid

https://www.lua.org/pil/8.4.html