How do I turn a string into an argument? - string

Question

I am using the app TouchLua.
I need to turn a string from a table into an argument. This is the only way I would like to do the table.
b = {}
b[1] = "010,010,draw.blue"
function drawButtons()
for i = 1,2 do
draw.fillrect(tonumber(string.sub(b[i],1,3)), tonumber(string.sub(b[i],5,7)), tonumber(string.sub(b[i],1,3))+10, tonumber(string.sub(b[i],5,7)),string.sub(b[i],9))
end
end
drawButtons()

Answer 1

Assuming you want a function eval so that print( eval( "draw.blue" ) ) is roughly equivalent to print( draw.blue ), here is a quick and dirty version:
local function eval( s, e )
return assert( load( "return "..s, "=eval", "t", e or _G ) )()
end
-- global variable
draw = { blue = 2 }
print( draw.blue )
print( eval( "draw.blue" ) )
If you are using an older Lua version than 5.2, you will need loadstring instead of load and an additional setfenv call. Of course, instead of using load you can parse the string s and index the table e or _G manually.
The above code assumes that draw is a global variable. If you want the code to work with a local variable you need to use the debug library:
-- same for local variable
local localdraw = { blue = 3 }
print( localdraw.blue )
-- needs debugging information, so won't work with stripped bytecode!
local function locals()
local t, i, n, v = {}, 1, debug.getlocal( 2, 1 )
while n ~= nil do
t[ n ], i = v, i+1
n, v = debug.getlocal( 2, i )
end
return t
end
print( eval( "localdraw.blue", locals() ) )