Lua Errors: Difference between revisions

* "Workspace.Script:2:" - The source of the error

* "attempt to ___" - The error is caused by the given operation on the wrong type of variable

! Operation Name !! Operator !! Allowed Types

|-

|-

| perform arithmetic || ''various'' || number, string*

| concatenate || '''..''' || string, number

|-

|}

** Note: String can only be used in arithmetic if it can be converted to a number.

Errors on the beginning of a line are often because an incomplete previous line.

In this case, the problems are:

Game.GetService -- missing parentheses ()

Game.GetService( -- missing close parenthesis )

Game:GetService -- missing parentheses () or "function arguments"

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{{ErrorMessage|Workspace.Script:3: '=' expected near '=='|}}

{{ErrorMessage|Workspace.Script:1: malformed number near '1..'|}}

This is caused by attempting to concatenate a number without putting a space since dots can be part of a number:

instead of

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{{ErrorMessage|Workspace.Script:1: bad argument #3 to '?' (Object expected, got function)|}}

{{ErrorMessage|Workspace.Script:1: bad argument #2 to '?' (string expected, got function)|}}

By indexing an object with the wrong type:

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{{ErrorMessage|Workspace.Script:1: bad argument #2 to '?' (Vector3 expected, got number)|}}

This error was caused by incorrect math on an Object

* Advanced Note: The message comes from the __add(obj,val) function in the Instance metatable.

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{{ErrorMessage|Part1 is not a valid member of Workspace|}}

Aside from the obvious, this message also occurs if you attempt to set a child directly:

You need to set the Name and Parent properties instead:

* Advanced Note: Why does this not have a source line?

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{{ErrorMessage|Workspace.Script:1: bad argument #1 to 'Lerp' (Vector3 expected, got userdata)|}}

Internally, Roblox objects use the [[userdata]] type of Lua. This means we've passed the wrong kind of object to the Lerp method.

== Unusual Error Messages ==

This is caused by too many events triggering each other.

A simple example is this script:

local bv = Instance.new("BoolValue")

bv.Parent = script

bv.Value = true

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{{ErrorMessage|Unable to cast value to std::string}}

Most common reason for this is passing nil or other Lua type to method expecting a string:

instead of  

-----

{{ErrorMessage|chunk has too many syntax levels}}

== Tricky Mistakes ==

[[Number|Floating point]] calculations can be surprising; it's safer to use inequalities. Or use an integer for controlling the loop.

n = 0

while true do

   if( n == 0.9 ) then break end -- never happens

end

Just like the number 1/3 would be 0.3333... (repeating) in decimal. The number 1/10 is 0.0<span style="text-decoration:overline;">0011</span> (repeating) in binary. Exact binary values are powers of 2, like 1/2, 1/4, 1/8, 1/16 etc. And multiples of those.

Since a computer must stop at a certain number of digits, the (repeating) idea is lost. If you add up 3 * 1/3, you get 0.999 instead of 1 or 10 * 1/10 in the computer is very close to 1 but not exactly. (In fact, it's so close to 1 that if you print it, it will say "1", but if you compare it with == or subtract it from one you'll see a slight difference).

part.Transparency = 0.1

if( part.Transparency == 0.1 ) then -- false

--

end

In this case, Transparency property of Roblox stores less digits than Lua uses.