Order indifferent local functions for cleaner code

mikatuo · December 18, 2022, 5:02pm

A topic for the feature request for a discussion.

Order indifferent local functions for cleaner code

opened 05:02PM - 18 Dec 22 UTC

feature request

**Is your feature request related to a problem? Please describe (REQUIRED):** I…t is cumbersome to write code in a more readable way so that the most important functions are placed at the top of a .script files and the least important ones at the bottom. The goal would be to place local functions in any order the developer wants. Furthermore, it is easy to place local functions in a wrong order and get runtime errors, like, `attempt to call global 'cap_max_speed' (a nil value)`. **Describe the solution you'd like (REQUIRED):** I would like to place all my local functions after the .script lifecycle methods (init, update, on_input, etc), and to place the high level functions at the top and the low level (smaller) ones at the bottom. As a bonus it would eliminate runtime errors, like, `attempt to call global 'cap_max_speed' (a nil value)` when mistakenly local functions are placed in an incorrect order. See "additional context" for a demo. **Describe alternatives you've considered (REQUIRED):** As a workaround I define local variables at the top of the .script file and then assign them at the end of the file, which allows to place them in any order. See "additional context" for a demo. **Additional context (OPTIONAL):** # Demo To demonstrate the problem, let's have a look at a refactored https://defold.com/examples/movement/move_forward/ example. Here is how one might clean up the .script file. Notice that you start reading the code from a low level function (`cap_max_speed`) and generally you will have to read through a mix of low and high level functions till the end of the file. Ideally, I would prefer to glance through the most important ones right after the .script file is opened, and then if I need, to read through the low level local functions. ![current](https://user-images.githubusercontent.com/7230306/208310070-d95075cf-b06b-4863-b3b8-bac43b12ccec.png) # Workaround As a workaround I can define all local functions at the top of the file, and then assign them in any order I like. While it works, it requires quite a lot of boilerplate code, adds "junk" variables at the beginning of the file and makes refactoring harder. ![workaround](https://user-images.githubusercontent.com/7230306/208310166-bdf5549b-2b8d-47fe-a3d8-051c99908b87.png) # Desired Solution The desired solution would be to place local functions anywhere in the file and in any order without any additional boilerplate code. ![goal](https://user-images.githubusercontent.com/7230306/208310212-6e0d644c-f7c2-49a5-88bd-428ac41bc0c3.png)

selimanac · December 18, 2022, 5:23pm

AFAIK this is a Lua thing not Defold.

WhiteBoxDev · December 18, 2022, 8:06pm

Agree with @selimanac. Would have to modify how Lua interpreter works, so I think this request is wishful thinking.

…but I also would like this to be added.

mikatuo · December 18, 2022, 8:40pm

I figured this is a Lua thing. There must be ways to achieve this as the script files are controlled by the engine, the question would be at what cost… I think that it will be totally worth it as it should ease the development process and improve code readability.

selimanac · December 19, 2022, 6:16am

Maybe it is possible for script files parsed by sdk. But I believe it require a lots of work and not even sure if it is necessary.
It is just how Lua works, functions are just variables in Lua.

What does it mean for functions to be “first-class values”? It means that, in Lua, a function is a value with the same rights as conventional values like numbers and strings.

https://www.lua.org/pil/6.html

mikatuo · December 19, 2022, 10:05am

I do think there are a lot of benefits. Not only it helps to organize the code better and make it cleaner, but it also helps to eliminate runtime errors when one accidentally places local functions incorrectly.

This seems doable. Even Editor extensions can read and modify project script files.

At this point I’m wondering are any major drawbacks in the workaround that I showed on Github (read below Option A and Option B).

Are here any Lua experts that can explain the difference between the following two approaches? Will Option B consume more memory because of closures, or will run noticeably slower? Or anything like that?

Option A

…

Option B

…

britzl · December 19, 2022, 10:08am

@mikatuo I wrote this in your feature request but thought I should replicate it here:

Thank you for a very well written feature request.

The problem you are describing is a problem with Lua, not with Defold. We use the LuaJIT or Lua 5.1.5 and both of these and the language itself actually care about the order in which functions are defined, or rather the order of variable definitions. We will not do anything on our end to address this as we do not consider it a problem which we can or should solve.

britzl · December 19, 2022, 10:14am

The difference is at what time during execution that the functions will be assigned to the variables:

-- these two are equivalent
-- on the next line of execution there will be a local
-- variable named foo that is assigned the function
local function foo() print("foo") end
local foo = function() print("foo") end

-- but this is obviously different

-- declare local foo with value nil
local foo

-- do something else
for i=1,100000 do
-- no-op, foo is still nil
end

-- assign foo with the anonymous function
foo = function() print("foo") end

-- now we can use foo
foo()

mikatuo · December 19, 2022, 10:22am

Thank you! Appreciate the explanation.