# Generator expressions support for BYPRODUCTS
**URL:** https://discourse.cmake.org/t/generator-expressions-support-for-byproducts/1124
**Category:** Development
**Created:** [April 30, 2020, 2:48pm UTC](https://discourse.cmake.org/t/generator-expressions-support-for-byproducts/1124 "2020-04-30T14:48:45Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@hsattler](https://discourse.cmake.org/u/hsattler)
#### Post date: [April 30, 2020, 2:48pm UTC](https://discourse.cmake.org/t/generator-expressions-support-for-byproducts/1124/1 "2020-04-30T14:48:45Z")
Hi,
I can add a custom POST\_BUILD command using generator expressions for the additional filename just fine. However, for Ninja to notice, I’d have to use BYPRODUCTS argument in the add\_custom\_command.
It is confusing that this does not understand generator expressions in this case. Why?
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### Author:  [@brad.king](https://discourse.cmake.org/u/brad.king)
#### Post date: [April 30, 2020, 2:59pm UTC](https://discourse.cmake.org/t/generator-expressions-support-for-byproducts/1124/2 "2020-04-30T14:59:14Z")
Generator expressions are not supported in custom command `OUTPUTS` or `BYPRODUCTS` (which are outputs that do not have to be newer than inputs). See [CMake Issue12877](https://gitlab.kitware.com/cmake/cmake/-/issues/12877). Some progress on that issue has been made within the last year. See [this discussion](https://gitlab.kitware.com/cmake/cmake/-/issues/12877#note_664330) in the issue for the current status.
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### Author:  [@hsattler](https://discourse.cmake.org/u/hsattler)
#### Post date: [April 30, 2020, 9:44pm UTC](https://discourse.cmake.org/t/generator-expressions-support-for-byproducts/1124/3 "2020-04-30T21:44:13Z")
This sounds like a lot of work. Actually I only needed it for stripping debug symbols. Having it set as BYPRODUCT is just cleaner but not technically necessary. Thanks.