Question

The output for the below script is:

AD[1] = [variable not found]
AD['2'] = bar

How can I modify the function getfield to return a value for v for both cases?

function getfield (f)
  local v = _G    
  for w in string.gfind(f, "[%w_]+") do
    v = v[w]
  end
 return v
end

AD = {[1] = 'foo', ['2'] = 'bar'}
data = {"AD[1]","AD['2']"}

for i,line in ipairs(data) do
  s = getfield(line)
  if s then
        print(line .. " = " .. s)
  else 
    print(line .. " = [variable not found]")
  end
end

UPDATE:
I’m 90% sure, this is going to work for me:

function getfield (f)
  local v = _G    
    for w in string.gfind(f, "['%w_]+") do
      if (string.find(w,"['%a_]")==nil) then
        w = loadstring('return '..w)()
      else 
        w = string.gsub(w, "'", "") 
      end
      v=v[w]
  end
  return v
end

Answer 1

This happens to work

function getfield (f)
  local v = _G    
  for w in string.gfind(f, "['%w_]+") do
    local x = loadstring('return '..w)()
    print(w,x)
    v = v[x] or v[w]
  end
 return v
end

AD = {[1] = 'foo', ['2'] = 'bar'}
data = {"AD[1]","AD['2']"}

for i,line in ipairs(data) do
  s = getfield(line)
  if s then
        print(line .. " = " .. s)
  else 
    print(line .. " = [variable not found]")
  end
end

but it’s pretty fragile.

Note that I added ' to the pattern.

The difficulty is that sometimes w is a string representing a name (key), and sometimes it’s a string representing a number. In the second case it needs to be converted from string to number. But you need the context or some syntax to decide.

Here’s the kind of fragility I mean:

>     data = {"math[pi]","AD['2']"}
>     
>     for i,line in ipairs(data) do
>>       s = getfield(line)
>>       if s then
>>             print(line .. " = " .. s)
>>       else 
>>         print(line .. " = [variable not found]")
>>       end
>>     end
math    table: 0x10ee05100
pi  nil
math[pi] = 3.1415926535898
AD  table: 0x10ee19ee0
'2' 2
AD['2'] = bar


> pi = 3
> math[3] = 42
>     data = {"math[pi]","AD['2']"}>
>     for i,line in ipairs(data) do
>>       s = getfield(line)
>>       if s then
>>             print(line .. " = " .. s)
>>       else 
>>         print(line .. " = [variable not found]")
>>       end
>>     end
math    table: 0x10ee05100
pi  3
math[pi] = 42
AD  table: 0x10ee19ee0
'2' 2
AD['2'] = bar

math[pi] is unchanged, but getfield interprets pi in the global context and gets 3 so the wrong field of math is returned.