Lua local question

[pancakepalace]

I don't think there is, but I don't see why this would be necessary. Just declare the variable at the top of the file.

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local b

function lol()
 b = somethingRather
end

I think this is the clearest way no. Declare variables in the scope that they will operate.

[Hydra]

I don't think there is, but I don't see why this would be necessary.

Depends on what you're doing, here's a small example:

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local x = 0

local Add = function(number)
	x = x + number
	return x
end

Is it the best example of a use for this? Not really, but you get the point.

[pancakepalace]

I'm not too sure what's the problem with your example.

[bartbes]

Yeah, you're asking us how to affect a 'file-local' local and then complaining it does? You lost me, anyway.

[Rad3k]

To clear up some confusion:
In Lua, accessing a table field always incurs some overhead - Lua has to find the key/value pair you're looking for. The more entries in that table, the larger the overhead (my guess is that it grows logarithmically). Like Lua manual says, global environment is an ordinary table, so each time you invoke a global variable, you're implicitly indexing a table. Now, if you declare some variable local, it's only accessible from its enclosing block, but the access to it is direct - it doesn't involve indexing any table. Also, each time you use 'local' keyword, you create a new local variable, even if there already exists a local variable with the same name. The old one will just become inaccessible.

As for function arguments - inside a function body, all the arguments are local variables. So, it's not only redundant to write:

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function fun (arg)
  local arg = arg or default_value
  do_stuff
end

but it's also undesirable - it needlessly creates another local variable. It's roughly equivalent to:

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function fun (arg1)
  local arg
  if arg1 then
    arg = arg1
  else
    arg = default_value
  end
  arg1 = nil
  do_stuff
end

Now, when you write:

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function fun (arg)
  arg = arg or default_value
  do_stuff
end

it's equivalent to

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function fun (arg)
  if arg then
    arg = arg
  else
    arg = default_value
  end
  do_stuff
end

Which, I believe, can be optimized by Lua compiler to just:

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function fun (arg)
  if not arg then
    arg = default_value
  end
  do_stuff
end

I hope it helps

[T-Bone]

I'm not too sure what's the problem with your example.

Yeah, you're asking us how to affect a 'file-local' local and then complaining it does? You lost me, anyway.

If you're talking to me, then first of all I'm not complaining. i was just wondering if there was syntax for declaring something "file-local". Turns out there isn't, which isn't a problem

[bartbes]

There is no such concept as a file, every file is just another block of code. So in the end what matters is where you define it/first use it.
As a language with lexical scoping it means it basically searches from the inside out, so where you last defined it as local, is what it will use. The solution to your 'problem' is indeed, to define the variable as local at the scope you want it, the file scope, in your case.

[T-Bone]

There is no such concept as a file, every file is just another block of code. So in the end what matters is where you define it/first use it.
As a language with lexical scoping it means it basically searches from the inside out, so where you last defined it as local, is what it will use. The solution to your 'problem' is indeed, to define the variable as local at the scope you want it, the file scope, in your case.

That post confused me. First you claim there is no such consept as a file, then you refer to "the file scope". If you declare something as local in one .lua file, can you still reach it from another? I'm still getting used to script languages so I get confused about stuff like this

[bartbes]

Like I said, a file is like any other chunk of code. You can see this with lua's loadfile and loadstring and love's love.filesystem.load, they all load the code into a function, so whatever is local there, in your case the file, is local to that 'function', and as such can't be accessed outside of the file.

[kraftman]

There is no such concept as a file, every file is just another block of code. So in the end what matters is where you define it/first use it.
As a language with lexical scoping it means it basically searches from the inside out, so where you last defined it as local, is what it will use. The solution to your 'problem' is indeed, to define the variable as local at the scope you want it, the file scope, in your case.

That post confused me. First you claim there is no such consept as a file, then you refer to "the file scope". If you declare something as local in one .lua file, can you still reach it from another? I'm still getting used to script languages so I get confused about stuff like this

No, if it's local to a file, it can't be reached by other files.