Control Flow

Ternary Operator

and .. or statement can be a replacement of ternary operator, but the trap here is, the expression after and must not ever return a falsy value. That is because the statment is not terminated when cond was met, it falls to expression after or.

-- first eval cannot be nil
local fn  = function()
    if cond then
        return true
    end
    return nil
end

_ = cond and fn() or canbe_nil -- canbe_nil might be picked when fn() returns falsy value which is unexpected

Safe Call

• pcall(fn: function, args: ...any): boolean, ...any

if pcall(function() error('foo') end) then
  print('not reachable here')
end

Local Scope

Use do .. end to create a isolated scope for certain operations.

do
  local foo = 'foo'
end

print(foo) -- Undefined global foo