Re: Capturing Lua variable as a string

[Romulo Bahiense <romulo@...>]

Julien Hamaide wrote:
> Lythoner LY wrote:
> > Hi All,
>> (snip)
> if you have a limited number of type, you can define them as global
> variable :
>
> INT = "INT"
> FLOAT = "FLOAT"
>
> function DEF_PARAM(v)
>    -- do something here to set NAME property from v
>    -- v["NAME"] = ???? How do I get string equivalent of variable v
>    return v
> end
>
> Just load this script before your definition file, and TYPE will
> automatically contain the text.

I think he meant the name of the variable:


>> In shell,
>>
>>> print(DeviceParam3.NAME)
>> DeviceParam3
>>
>>> print (type(DeviceParam3.NAME)
>> string


Unfortunately, it is not possible to know what is the name of the 
variable you are assigning to (inside the DEF_PARAM function, of 
course). What I suggest, is to __newindex the chunk's environment and 
post-assign the name. Something like:


myconfiguration.lua:
DeviceParam1 = DEF_PARAM{ TYPE = INT }
DeviceParam2 = DEF_PARAM{ TYPE = INT }
DeviceParam3 = DEF_PARAM{ TYPE = INT }

~~ end of myconfiguration.lua:


configloader.lua
function load( filename )
    local f = assert( loadfile( filename ) )
    local e = setmetatable( {}, {
        __index = _G;
        __newindex = function( t, k, v )
            if type( k ) == 'string' and type( v ) == 'table' then
                v.NAME = k
            end
        end; } )
    setfenv( f, e )
    f()
end

~~ end of configloader.lua

Of course, this will cause all assignments of tables to global variables 
 be changed. You can make some tricks to only assign the NAME fields to 
a particular subset. First, you can check for the presence of a TYPE 
attribute as a pre-condition (trivial). Second, you can store the newly 
created table in another table while creating it with DEF_PARAM and then 
check if the table being assigned belongs to it:

configloader2.lua
function load( filename )
    local f = assert( loadfile( filename ) )

    local t = {}
    local old_DEF_PARAM = DEF_PARAM

    local e = setmetatable(
        {
            DEF_PARAM = function( info )
                -- In case DEF_PARAM creates another table...
                info = old_DEF_PARAM( info )
                t[ info ] = true
                return info
            end;
        }, {
            __index = _G;
            __newindex = function( t, k, v )
                if t[ v ] then
                    v.NAME = k
                end
            end;
        }
    )
    setfenv( f, e )
    f()
end

~~ end of configloader2.lua

Hope that helps,

--rb