# Math Expressions cannot use variables from hidden categories

**URL:** <https://forums.unrealengine.com/t/math-expressions-cannot-use-variables-from-hidden-categories/344981>\
**Category:** Blueprint\
**Tags:** math-expression, unreal-engine, Blueprint, question\
**Created:** [January 22, 2016, 8:56pm UTC](https://forums.unrealengine.com/t/math-expressions-cannot-use-variables-from-hidden-categories/344981 "2016-01-22T20:56:10Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![manoelneto](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@manoelneto](https://forums.unrealengine.com/u/manoelneto)\
**Post date:** [January 22, 2016, 8:56pm UTC](https://forums.unrealengine.com/t/math-expressions-cannot-use-variables-from-hidden-categories/344981/1 "2016-01-22T20:56:10Z")

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Hi,

I have some blueprints with transient properties that are used internally and I add them to a category that is hidden by using the Hide Categories list in the class settings. This is done so they don’t show up in the detail/default panes and confuse our designers (we only want the variables they need to work with to be visible).

The problem is that this breaks any math expression that uses those variables causing a “cannot access ‘VariableName’ variable from the expression” error. I expected the hideCategories list to be merely a visual thing, but seems it actually affects compilation.

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**Author:** ![anonymous\_user\_b9532c9a](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@anonymous\_user\_b9532c9a](https://forums.unrealengine.com/u/anonymous_user_b9532c9a)\
**Post date:** [January 24, 2016, 8:09pm UTC](https://forums.unrealengine.com/t/math-expressions-cannot-use-variables-from-hidden-categories/344981/2 "2016-01-24T20:09:21Z")

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Hi ,

Unfortunately, I have not been able to reproduce this on my end. I set several variables to a hidden category and plugged them into a math expression node, however they were still read as I would expect.

- Do you have any specific steps I can take to reproduce this error on my end?
- Does this occur in a clean, blank project with no additional content or is it limited to one project?

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**Author:** ![anonymous\_user\_b9532c9a](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@anonymous\_user\_b9532c9a](https://forums.unrealengine.com/u/anonymous_user_b9532c9a)\
**Post date:** [January 28, 2016, 8:29pm UTC](https://forums.unrealengine.com/t/math-expressions-cannot-use-variables-from-hidden-categories/344981/3 "2016-01-28T20:29:37Z")

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Hi ,

We have not heard from you in several days. I am marking this as answered for tracking purposes. If you are still experiencing this error, please comment with the requested information.

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**Author:** ![manoelneto](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@manoelneto](https://forums.unrealengine.com/u/manoelneto)\
**Post date:** [January 29, 2016, 2:35pm UTC](https://forums.unrealengine.com/t/math-expressions-cannot-use-variables-from-hidden-categories/344981/4 "2016-01-29T14:35:38Z")

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I managed to reproduce it on the launcher version of 4.10.2:

- Create a new blueprint class
- Create a variable called “Foo”, set its type to integer
- Set Foo’s category to “Bar”

[http://i.imgur.com/wbRfcBd.png](http://i.imgur.com/wbRfcBd.png)

- Go to the class settings, add “Bar” to the “Hide Categories” list

[http://i.imgur.com/89WAxHX.png](http://i.imgur.com/89WAxHX.png)

- Create a math expression like “Foo + 1”
- The expression will not compile:

[http://i.imgur.com/FEY0Z5o.png](http://i.imgur.com/FEY0Z5o.png)

Here’s an empty project which shows the problem:  
[link text][4]

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<div class="post-metadata">

**Author:** ![anonymous\_user\_b9532c9a](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@anonymous\_user\_b9532c9a](https://forums.unrealengine.com/u/anonymous_user_b9532c9a)\
**Post date:** [January 29, 2016, 3:17pm UTC](https://forums.unrealengine.com/t/math-expressions-cannot-use-variables-from-hidden-categories/344981/5 "2016-01-29T15:17:55Z")

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Hi ,

I was able to reproduce this error on my end and have entered a bug report, UE-26208, to be assessed by the development staff.