Lua: Concise expression of table scope

Question

I'm working on a game where a bunch of characters will be generated on the fly, based on some constraints defined either in the project or externally via mod files. I am using MoonSharp Lua (5.2) interpreter for interfacing with my C# code, and Lua tables to store the constraint presets. As an example:

require "Defaults"
AgePresets = {}

-- Single value
AgePresets.Newborn = 0

-- Simple ranges
AgePresets.Default = defaultAgeRange --referring to the Defaults require
AgePresets.Child = {1, 12} 
AgePresets.Teenager = {13, 19}
AgePresets.YoungAdult = {20, 29}
AgePresets.Adult = {30, 40}
AgePresets.MiddleAge = {40, 60} 
AgePresets.Senior = {61, 80}
AgePresets.Elder = {81, 99}
AgePresets.Methuselah = {100, 150}  
AgePresets.Methuselah2 = {150, 200}

-- Weighted ranges // again referring to previously defined elements to keep things concise
AgePresets.Tween = {
            {weight = 1, minmax = AgePresets.Teenager },
            {weight = 1, minmax = AgePresets.YoungAdult }
         }

This works fine, but from an end-user point of view, there's a lot of unnecessary typing involved. We are clearly working on AgePresets here but it is still mentioned as a prefix before every member name.

I could of course define AgePresets as an array, like AgePresets = { Child = {}, Teenager = {} } but the problem with that is then I cannot refer to previously defined elements in the array.

This doesn't work:

AgePresets = {
    Child = {1,12},
    RefToChild = Child, //attempt to index a nil value exception
    Teen = {13,19}
}

What I ideally want to achieve is a clean, concise way for users to enter this data in, like in the first example but without having to put AgePresets. prefix before everything. How do I go about declaring a scope in a file such that all succeeding members defined in the file will be within that scope, while maintaining the ability to refer to other members defined previously in the scope?

5.2, sorry I forgot to mention it. Added it to the question now. — TaylanK, Jun 20 '17 at 20:56

score 1 · Accepted Answer · answered Jun 20 '17 at 21:36

1

AgePresets = setmetatable({}, {__index = _G})

do
   local _ENV = AgePresets
   Newborn = 0
   Child = {1,12}
   RefToChild = Child -- this ref is Ok
   Teen = {13,19}
   YoungAdult = {20,29}
   Tween = {
      {weight = 1, minmax = Teen },
      {weight = 1, minmax = YoungAdult }
   }
   rnd = math.random(10)   -- global functions are available here
end

setmetatable(AgePresets, nil)

answered Jun 20 '17 at 21:36

Egor Skriptunoff

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Thanks a lot! I took the extra step of putting everything other than data definitions in string constants on the C# side, and using string formatter to procedurally build the appropriate Lua syntax based on file name. Now it looks just the way I wanted. :) – TaylanK Jun 20 '17 at 22:51

score 0 · Answer 2 · answered Jun 22 '17 at 22:33

You can mix the two styles: table constructor for fields that don't need to reference variables that aren't in scope yet, followed by assignment statements for the rest.

I would do that unless the order of the fields in the code significantly enhanced comprehension.

Lua: Concise expression of table scope

2 Answers2