Global Functions: Difference between revisions

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== Introduction ==
== Introduction ==
Have you ever wondered how things like :Remove() and :Clone() always work, even though you've never indexed it? Here's how.
Global functions are function accessible in all environments and threads.  Global functions must be contained within what is called the global environment which is represented by a table called the global table.  _G is the variable that holds the global table.  In ROBLOX _G works differently than in normal Lua.  In ROBLOX you must index values from the global table if you set them.


== How a global command works ==
{{Example|<syntaxhighlight lang="lua">
_G["foo"] = "bar"
print(_G["foo"]) -- bar
</syntaxhighlight>}}


If you know how to use the _G[] (global) command, this might come more easily to you than others. This is basically how a global command works:
Any function, and any thread can access the "foo" variable so long as the example code is run before the other thread is executed.


<pre>_G["Bob"] = game.Workspace.Bob</pre>
== History ==
Sometime in 2010 it was decided that _G was a security issue.  Before this date all threads could read and write to the global table.  Instead, a substitute table was put in place of _G.  This was a table called "shared". All threads could access the "shared" table, however you must actually index it:


If you're in a ScriptBuilder, you can exit that script and open a new one. Put this in it:
{{Example|<syntaxhighlight lang="lua">
shared["foo"] = "bar"
print(shared["foo"]) -- bar
</syntaxhighlight>}}


<pre>Bob.Torso:Remove()</pre>
The way _G worked before allowed this:


run that script, and Bob's torso gets removed! Why? Because the _G[] (global) command makes "Bob" available in every script.
{{Example|<syntaxhighlight lang="lua">
_G["foo"] = "bar"
print(foo) -- bar
</syntaxhighlight>}}


== Getting a global function ==
Values within the _G table would be replicated into all the threads environments, not just the _G table itself.
 
<pre>
_G["Lazer"] = function(person)
person.Torso:Remove()
end
</pre>
 
Now exit that script, and run this script:
 
<pre>Lazer(game.Workspace.Bob)</pre>
 
If your character's name is "Bob," you should have your torso removed.


[[Category:Scripting Tutorials]]
[[Category:Scripting Tutorials]]

Latest revision as of 04:53, 27 April 2023

Up one category:
Tutorials

Introduction

Global functions are function accessible in all environments and threads. Global functions must be contained within what is called the global environment which is represented by a table called the global table. _G is the variable that holds the global table. In ROBLOX _G works differently than in normal Lua. In ROBLOX you must index values from the global table if you set them.

Example
_G["foo"] = "bar"
print(_G["foo"]) -- bar


Any function, and any thread can access the "foo" variable so long as the example code is run before the other thread is executed.

History

Sometime in 2010 it was decided that _G was a security issue. Before this date all threads could read and write to the global table. Instead, a substitute table was put in place of _G. This was a table called "shared". All threads could access the "shared" table, however you must actually index it:

Example
shared["foo"] = "bar"
print(shared["foo"]) -- bar


The way _G worked before allowed this:

Example
_G["foo"] = "bar"
print(foo) -- bar


Values within the _G table would be replicated into all the threads environments, not just the _G table itself.

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