# Using isdefined to check where a function is defined

**URL:** <https://discourse.julialang.org/t/using-isdefined-to-check-where-a-function-is-defined/37536>\
**Category:** General Usage\
**Tags:** cxx\
**Created:** [April 13, 2020, 11:18pm UTC](https://discourse.julialang.org/t/using-isdefined-to-check-where-a-function-is-defined/37536 "2020-04-13T23:18:42Z")\
**Posts on this page:** 1\
**Showing post:** 5

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**Author:** ![yuyichao](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/yuyichao/32/20_2.png) [@yuyichao](https://discourse.julialang.org/u/yuyichao)\
**Post date:** [April 14, 2020, 5:00am UTC](https://discourse.julialang.org/t/using-isdefined-to-check-where-a-function-is-defined/37536/5 "2020-04-14T05:00:02Z")

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In another word,

1. There’s nothing special about included file.
2. The error you get in [Trying not to overload Base.open - #2 by Sukera](https://discourse.julialang.org/t/trying-not-to-overload-base-open/37432/2) is entirely expected and there’s no way around it. You should not change the behavior based on if something has been used or not to avoid the error. This error has to be fixed by the user. Trying to be smart here is bad.

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_[View the full topic](https://discourse.julialang.org/t/using-isdefined-to-check-where-a-function-is-defined/37536)._