Re: How to check for key existence in a table (for the lazy programmer) ?

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

On Saturday, January 31, 2015, Bertrand Mansion <lua@mamasam.net> wrote:
> In Lua programs, I often see code like the following:
>
>   if host.devices and host.devices.bridge and host.devices.bridge.friendlyName then
>
> In Php, I have seen this:
>
>   if (isset($host['devices']['bridge']['friendlyName']))
>
>
> In Python, I have seen this:
>
>   try:
>     if host['devices']['bridge']['friendlyName']:
>       ...
>   except KeyError:
>     pass
>
> Are there other ways in Lua to check for a key existence ?

Another way is to use a vararg function:

local function pindex(tbl, key, ...) 

    tbl = tbl[key]

    If (...) then

        If type(tbl) == "table" then

            return pindex(tbl, ...)

        else

            return nil, tbl, key

        end

     else

         return true, tbl

     end

end

local success, value, failed_at = pindex(my_table, "foo", "bar", "baz")

(iPhone + Gmail is not awesome as a code editor. Ymmv. Also, others may have a faster way)

-Andrew