4.6 KiB
permalink | title | toc |
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/getting-started | Getting Started | true |
To get started with Luau you need to install Roblox Studio, which you can download here.
Creating a place
If you just want to experiment with the language itself, you can create a simple baseplate game.
![](/michael/luau/media/commit/710547df837f71214874ce6eaf50908389d32f88/docs/_pages/%7B%7B%20site.url%20%7D%7D%7B%7B%20site.baseurl%20%7D%7D/assets/images/create-new-place.png)
Creating a script
To create your own testing script, go to ServerScriptService in the explorer tree and add a Script object.
![](/michael/luau/media/commit/710547df837f71214874ce6eaf50908389d32f88/docs/_pages/%7B%7B%20site.url%20%7D%7D%7B%7B%20site.baseurl%20%7D%7D/assets/images/create-script.png)
Double-click on the script object and paste this:
function ispositive(x)
return x > 0
end
print(ispositive(1))
print(ispositive("2"))
function isfoo(a)
return a == "foo"
end
print(isfoo("bar"))
print(isfoo(1))
Note that there are no warnings about calling ispositive()
with a string, or calling isfoo()
a number.
Type inference
Now modify the script to include --!strict
at the top:
--!strict
function ispositive(x)
return x > 0
end
print(ispositive(1))
print(ispositive("2"))
function isfoo(a)
return a == "foo"
end
print(isfoo("bar"))
print(isfoo(1))
In strict
mode, Luau will infer types based on analysis of the code flow. There is also nonstrict
mode, where analysis is more conservative and types are more frequently inferred as any
to reduce cases where legitimate code is flagged with warnings.
In this case, Luau will use the return x > 0
statement to infer that ispositive()
is a function taking an integer and returning a boolean. Similarly, it will use the return a == "foo"
statement to infer that isfoo()
is a function taking a string and returning a boolean. Note that in both cases, it was not necessary to add any explicit type annotations.
Based on Luau's type inference, the editor now highlights the incorrect calls to ispositive()
and isfoo()
:
![](/michael/luau/media/commit/710547df837f71214874ce6eaf50908389d32f88/docs/_pages/%7B%7B%20site.url%20%7D%7D%7B%7B%20site.baseurl%20%7D%7D/assets/images/error-ispositive.png)
![](/michael/luau/media/commit/710547df837f71214874ce6eaf50908389d32f88/docs/_pages/%7B%7B%20site.url%20%7D%7D%7B%7B%20site.baseurl%20%7D%7D/assets/images/error-isfoo.png)
Annotations
You can add annotations to locals, arguments, and function return types. Among other things, annotations can help enforce that you don't accidentally do something stupid. Here's how we would add annotations to ispositive()
:
--!strict
function ispositive(x : number) : boolean
return x > 0
end
local result : boolean
result = ispositive(1)
Now we've told explicitly told Luau that ispositive()
accepts a number and returns a boolean. This wasn't strictly (pun intended) necessary in this case, because Luau's inference was able to deduce this already. But even in this case, there are advantages to explicit annotations. Imagine that later we decide to change ispositive()
to return a string value:
--!strict
function ispositive(x : number) : boolean
if x > 0 then
return "yes"
else
return "no"
end
end
local result : boolean
result = ispositive(1)
Oops -- we're returning string values, but we forgot to update the function return type. Since we've told Luau that ispositive()
returns a boolean (and that's how we're using it), the call site isn't flagged as an error. But because the annotation doesn't match our code, we get a warning in the function body itself:
![](/michael/luau/media/commit/710547df837f71214874ce6eaf50908389d32f88/docs/_pages/%7B%7B%20site.url%20%7D%7D%7B%7B%20site.baseurl%20%7D%7D/assets/images/error-ispositive-string.png)
The fix is simple; just change the annotation to declare the return type as a string:
--!strict
function ispositive(x : number) : string
if x > 0 then
return "yes"
else
return "no"
end
end
local result : boolean
result = ispositive(1)
Well, almost - since we declared result
as a boolean, the call site is now flagged:
![](/michael/luau/media/commit/710547df837f71214874ce6eaf50908389d32f88/docs/_pages/%7B%7B%20site.url%20%7D%7D%7B%7B%20site.baseurl%20%7D%7D/assets/images/error-ispositive-boolean.png)
If we update the type of the local variable, everything is good. Note that we could also just let Luau infer the type of result
by changing it to the single line version local result = ispositive(1)
.
--!strict
function ispositive(x : number) : string
if x > 0 then
return "yes"
else
return "no"
end
end
local result : string
result = ispositive(1)
Conclusions
This has been a brief tour of the basic functionality of Luau, but there's lots more to explore. If you're interested in reading more, check out our main reference pages for syntax and typechecking.