Re: Locking Table Member Additions

[Tim Hill <drtimhill@...>]

On Jun 17, 2014, at 10:04 AM, Leinen, Rick <RLeinen@leviton.com> wrote:

> Thanks for your reply Sean.
> 
> Yes, I know Lua typically starts arrays with a 1.  Old habits die hard. :-)  I put the nil assignment there as a flag.  Maybe that's not necessary.  I'll explore that.
> 
> Yes, creating the table in C is more work.  I have a couple of reasons for exploring this option.
> 	1) Lua is new to our company.  We are hoping that it will allow us to place the functionality of the product in a Lua script rather than hardcoded in C/C++. This will make it much easier to change or add functionality, even in the field.  As a result, there may be occasion where our field service engineers may make modifications.  Since none of the staff are coding experts, I want to hide as much of the nitty-gritty stuff as possible.  That is the reason I would like to lock the members of the table.  Less chance for mistakes.
> 	2) The Kinetis microcontroller I am targeting has 1MB of internal flash and 256KB of internal SRAM.  Neither is a lot, but I have much more flash.  By defining the table in C, I am hoping that I will be using less RAM since the Lua script will be smaller.  This may prove out to be negligible, but that is the thinking at the time.
> 
> I'll have to study your suggestions a bit, as I am fairly new to Lua, especially the C side.
> 
> Thanks again,
> 
> Rick Leinen
> Engineering Manager, R&D Projects
>   
> Lighting and Energy Solutions
> 
> T: 503 404-5561 F: 503 404-5661 C: 503 860-6305
>   

Couple of things to note. Byte-for-byte, compiler Lua code is very compact. You might find the Lua code to build the table is smaller than the equivalent C code. As others have noted, you might be better served by validating the table when passed to a C function, rather than trying to lock it down proactively (again, probably less code overall to do this).

—Tim