Grimmys: Add LUA tutorial category

2024-03-11T19:25:43Z

Add LUA tutorial category

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	As you can see with the example_thing() function above, proper indentation is a GREAT way to visibly see scopes and quickly tell where a variable is and isn’t available.		As you can see with the example_thing() function above, proper indentation is a GREAT way to visibly see scopes and quickly tell where a variable is and isn’t available.

			[[Category:Lua Tutorials]]

Vandy: Created page with "A super important concept in Lua is the concept of ''scope''. Every single variable made has a ''scope'', which is used to define where a variable can be accessed. By default..."

2021-02-07T18:40:19Z

Created page with "A super important concept in Lua is the concept of ''scope''. Every single variable made has a ''scope'', which is used to define where a variable can be accessed. By default..."

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A super important concept in Lua is the concept of ''scope''. Every single variable made has a ''scope'', which is used to define where a variable can be accessed.

By default, all variables are <code>global</code>, which means they’re in the entire global environment. The global environment is a slightly-fancy way of saying “available within the entire program”. When writing Total War scripts, it’s a little suboptimal to use global variables, for a few reasons – 1) What if someone else wants to use a variable named <code>a</code>, and you do as well? This would force you to have a fully unique name for every single variable everywhere. Kinda a pain! 2) Saving that variable globally is taking up memory, since that variable will never be destroyed. It will take a lot of work to actually cause performance issues, but it’s good to be mindful of. 3) What if we want our variable to be a secret? Huh? They can’t get our birthday present! ''gollum''

And all this is where the keyword <code>local</code> comes in. The <code>local</code> keyword defines a specific scope for a variable, and prevents them from being a global variable.
<code>function example()
local var = "Hello World!"
out(var)
end

example() → Hello World!
out(var) → nil -- the variable "var" doesn't exist here!</code>
In this example, the variable <code>var</code> is defined within the function <code>example</code>‘s definition. That means that <code>var</code> is only available from ''where it is defined'' (ie. local var =) to ''where the scope ends''. In this case, the scope ''ends'' at the <code>end</code> keyword.

This is as good a time as any to look at the other ways scope can be defined. A variable can be scoped to the ''root'' of a script, or any number of nestled scopes within that root.

Other key-words other than <code>function</code> that define a scope (and their end point) are as follows:

* do –<nowiki>[[ the scope ]]</nowiki> end
* function function_name() –<nowiki>[[ the scope ]]</nowiki> end
* if –<nowiki>[[ whatever ]]</nowiki> then –<nowiki>[[ the scope ]]</nowiki> end
* while –<nowiki>[[ whatever ]]</nowiki> then –<nowiki>[[ the scope ]]</nowiki> end

Let’s take a slightly-complicated look at that:
<code>local a = 5 -- visible to everything BELOW this line!

function example_thing()
local b = a -- visible to everything BELOW this line, until the "end" that matches "function"
do
local c = 15 -- visible to everything BELOW this line, until the "end" that matches "do"
out(c) → 15
out(b) → 5
end
out(b) → 5
-- c is NOT available here!
end

-- b and c are NOT available here!
out(a) → 5</code>
This is a good point as any to explain two things, and issue two directives:

# ALWAYS use the keyword <code>local</code>.
# ALWAYS use good indentations! Scopes should be easily detected.

Be smart with where exactly the term “local” is used – you’ll pick up how later on as you go and pick my brain, but for now, understand that you must ALWAYS put the keyword <code>local</code> before a variable!

As you can see with the example_thing() function above, proper indentation is a GREAT way to visibly see scopes and quickly tell where a variable is and isn’t available.

Lua:Scopes & Stuff - Revision history

Grimmys: Add LUA tutorial category

Vandy: Created page with "A super important concept in Lua is the concept of ''scope''. Every single variable made has a ''scope'', which is used to define where a variable can be accessed. By default..."