# Why \`const\` fields in a \`mutable struct\` instead of \`mutable\` field in ordinary \`struct\`?

**URL:** <https://discourse.julialang.org/t/why-const-fields-in-a-mutable-struct-instead-of-mutable-field-in-ordinary-struct/103454>\
**Category:** Internals & Design\
**Created:** [September 1, 2023, 7:00pm UTC](https://discourse.julialang.org/t/why-const-fields-in-a-mutable-struct-instead-of-mutable-field-in-ordinary-struct/103454 "2023-09-01T19:00:33Z")\
**Posts on this page:** 1\
**Showing post:** 8

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**Author:** ![Zach\_Christensen](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/zach_christensen/32/7220_2.png) [@Zach\_Christensen](https://discourse.julialang.org/u/Zach_Christensen)\
**Post date:** [September 2, 2023, 1:51am UTC](https://discourse.julialang.org/t/why-const-fields-in-a-mutable-struct-instead-of-mutable-field-in-ordinary-struct/103454/8 "2023-09-02T01:51:28Z")

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I’m pretty sure this is the main reason but I’m not sure if it’s documented anywhere. It seems like a good performance tip or maybe just part of the const docstring

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_[View the full topic](https://discourse.julialang.org/t/why-const-fields-in-a-mutable-struct-instead-of-mutable-field-in-ordinary-struct/103454)._