Generate dependencies for Lua?

Question

I have a lua project with lua files specified in multiple directories all under the same root folder with some dependencies.

Occasionally I run into issues where when a table is being loaded at load time I get a nil exception as the table is referencing a not yet initialised table, like:

Customer = 
{
     Type = CustomerTypes.Friendly
}

Which causes a nil exception for CustomerTypes as CustomerTypes.lua has not yet loaded.

My current solution is to simply have a global function call in these lua files to load the dependency scripts.

What I would like to do is pre-process my lua files to find all dependencies and at run time load them in that order without needing function calls or special syntax in my lua files to determine this (i.e. the pre-processor will procedurally work out dependencies).

Is this something which can be realistically achieved? Are there other solutions out there? (I've come across some but not sure if they're worth pursuing).

As an alternative, consider designing the dependencies to be compatible with require and actually "declaring" every dependency of each file in the file itself with require calls (typically in the form of local CustomerTypes = require("CustomerTypes") together near the top of a file). — Tom Blodget

zeromus zeromus · Accepted Answer · 2016-07-20T07:05:55

As usual with lua there are about 230891239122 ways to solve this. I'll name 3 off the top of my head but I bet I could illustrate at least 101 of them and publish a coffee table book.

First of all, it must be said that the notion of 'dependencies' here is strictly up to your application. Lua has no sense of it. So this isn't anything like overcoming a deficiency in lua, it's simply you creating a scripting environment in your application that makes you comfortable, and that's what lua's all about.

Now, it seems to me you've jumped to a conclusion that preprocessing is required to solve the given problem. I don't think that's warranted. I feel somewhat comfortable saying a more conventional approach to solving the problem would be to make a __newindex metamethod globally which handles the "CustomerTypes doesnt exist yet" situation by referencing a list of scripts which have been scanned out of the filesystem initially for one called CustomerTypes.lua and running that.

But maybe you have some good reason for wanting it done strictly as preprocessing. In your case, I would start by considering 'dependencies' to be any name which is a script found in your scripts filesystem. Then scan each script to look for the names of dependencies using the definitions/list you just created, and prepend a load(dependency) command to each of those scripts.

Since the concept of "runtime" or "preprocessing" is somewhat ambiguous in this context, you might mean at script-compile-time. You could use the LuaMacros token filters system to effect a macro which replaces CustomerTypes with require("CustomerTypes.lua") or something to that effect after having discovered that CustomerTypes is a legal dependency name.

Generate dependencies for Lua?

1 Answers