Re: Privately patching strings lib in Lua 5.2

[Andrew Starks <andrew.starks@...>]

On Friday, December 20, 2013, Hisham  wrote:
> On 20 December 2013 13:58, Andrew Starks <andrew.starks@trms.com> wrote:
>
> > ```lua
> > _ENV = {
> >   print = print, string = string, table = table, pairs = pairs, type = type
> > }
> >
> > do
> >   local _string = string
> >   local concat = table.concat
> >   string = {}
> >   for m_name, m_func in pairs(_string) do
> >     string[m_name] = m_func
> >   end
> >
> >   function string:map(...)
> >     local args = type(...) == "table" and (...) or {...}
> >
> >     return self .. concat(args, self)
> >
> >   end
> >
> >
> > end
> > --testing
> > --This is result that I want.
> > print(string.map("test","this", "that"))
> > -->testthistestthat
> >
> > --This is the syntax that I want to use, but it doesn't work...
> > print(("test"):map("this", "that"))
> > --lua: ...src\testing\test_string_library_question.lua:23: attempt to
> > call method 'map' (a nil value)
> > ```
> > If I skip the parts where I hide my change from the global
> > environment, then both function calls behave identically.
> >
> > Is there a way to patch the `string` library so that the changes apply
> > to strings using the `self`/colon method, without patching `string`
> > globally? Debug library?
>
> All strings share the same metatable, which is a table whose __index
> points to the `string` table:
>
> > print(string)
> table: 0x9d35000
> > print( debug.getmetatable("hello") )
> table: 0x9d34e88
> > print( debug.getmetatable("world") )
> table: 0x9d34e88
> > print( debug.getmetatable("world").__index )
> table: 0x9d35000
>
> So yes, you can alter the behavior of strings' colon behavior without
> patching `string` globally:
>
> > print(("hello"):find("e"))
> 2    2
> > another = {}; debug.setmetatable("world", { __index = another })
> > print(("hello"):find("e"))
> stdin:1: attempt to call method 'find' (a nil value)
>
> ...but that introduces a global change to your environment, anyway.
>
> -- Hisham

Yeah. I confirmed that by just remembering the shared metatable thing, but was hoping that I had forgotten about some other kind if magic. Your confirmation is helpful and thank you for the follow up!

-Andrew