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- Subject: Re: Say No to global-by-default
- From: Jakub Jirutka <jakub@...>
- Date: Wed, 4 Jul 2018 21:06:47 +0200
I completely agree with the proposal and all the points why it's needed.
- very well written!
"global by default", specifically defining variable as global by default
(and also no difference between declaring global variable and
reassignment of any variable), is one of the few ugly sides of Lua.
Solving this problem would make Lua much better language.
I have just one concern - backward compatibility with existing Lua
modules. If I as a Lua programmer want to require some possibly outdated
third-party Lua modules, there should be a way how to make it work on
newer Lua with the said feature without modifying the original sources.
There are multiple ways how to achieve that:
- make the new feature *opt-in* per file using some "magic" comment or
string at top of the file,
- make the new feature *opt-out* per file using e.g. extra argument for
the require() function (and lower-level functions for loading chunks as
- make the new feature opt-in or opt-out globally using lua(1) CLI
option or some global variable (this would be probably the easiest one,
but also the one I'd strongly discourage for multiple reasons)
- some different way?
(I didn't read these dozens following messages, so I'm sorry if
repeating what someone else already said.)
On 04/07/18 07:26, Egor Skriptunoff wrote:
> Let me start (n+1)-th thread about "global by default" feature of Lua.
> My suggestion is to replace "global by default" approach with "nothing
> by default" by introducing special syntax for accessing global variables:
> $print("Hello world") -- ok
> print("Hello world") -- syntax error: referencing undeclared
> variable "print"
> _G.print("Hello world") -- syntax error: referencing undeclared
> variable "_G"
> "$" is not a part of an identifier.
> "$" is a lexem (for example, there could be a space between "$" and
> global variable name).
> "$" is absolutely the same as "_ENV." but is more comfortable to use.
> Why do we need this?
> "$globalvar" notation introduces two separate namespaces: one for
> globals and one for locals/upvalues.
> As a result of this separation, most of variable name typos will be
> detected at compile time.
> Although global name typos will not be detected ($math.sin ->
> $moth.sin), the most of identifiers in properly-written Lua programs are
> Currently, writing Lua programs without "global-nil-alarmer" (such as
> "strict.lua") is practically impossible (because typos in local variable
> names are silently converted to globals).
> "$print" contains more symbols than "print", and you have to press SHIFT
> on your keyboard to type "$", but this is not a drawback.
> Instead, there is a point in it: users would have to pay attention to
> slow global access.
> More finger moves = more CPU time to access.
> So, we are adding "ergonomical motivation" to cache globals in Lua
> programs :-)
> Polluting of global namespace is already discouraged in Lua, so
> introducing "$" prefix for globals is the next step in that direction.
> It is a polite way to say: "use globals only when they are really needed".
> The "$globalvar" notation will solve problem with globals occasionally
> shadowed out by locals or upvalues:
> local function sort_desc(table)
> table.sort(table, function(a, b) return a>b end) -- very popular
> newcomers' mistake
> The "$globalvar" notation will make the difference between
> "monkey-patch-friendly code" and "monkey-patch-unfriendly code" more
> easy to see.
> BTW, "_ENV" could be removed from Lua as "$" could do the same (with
> some modifications in the parser to interpret "$" either as "_ENV." or
> as "_ENV"):
> $print() -- instead of print()
> $.print() -- instead of print()
> local env = $ -- instead of local env = _ENV
> $[key] = value -- instead of _ENV[key] = value
> function sndbx($) -- instead of function sndbx(_ENV)
> What are your thoughts on this?
> -- Egor