Question

I’m learning Lua from a book, which is a bit old.
I’ve tried searching the web, but because of the use of the # sign in my search I get really confusing results.

It says that in order to use upvalue you need to use the % sign.

But when I write it in my code I get an error.

Account.new = function (starting_balance)
  local self = {}
  local balance = starting_balance

  self.withdraw = function (v)
    %balance = %balance - v;
  end
  return self
end

error is : unexpected symbol near '%'

Is there a new way to handle upvalues in Lua 5.x ?

Answer 1

Since Lua 5.0, there is no more such thing as a “upvalue sign”. An upvalue is a local to the environment a function is declared in, and as such can simply be accessed as any other local variable.

In your case: just use balance instead of %balance.

From Lua 5.1, % is used as modulo operator.

A good but slightly outdated book is the online available version of Programming in Lua, and of course, the reference manual.