# Automatically parameterizing a type

**URL:** <https://discourse.julialang.org/t/automatically-parameterizing-a-type/15945>\
**Category:** Performance\
**Created:** [October 5, 2018, 7:20pm UTC](https://discourse.julialang.org/t/automatically-parameterizing-a-type/15945 "2018-10-05T19:20:42Z")\
**Posts on this page:** 1\
**Showing post:** 6

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**Author:** ![stevengj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stevengj/32/71_2.png) [@stevengj](https://discourse.julialang.org/u/stevengj)\
**Post date:** [October 7, 2018, 12:20pm UTC](https://discourse.julialang.org/t/automatically-parameterizing-a-type/15945/6 "2018-10-07T12:20:31Z")

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Concrete struct field types are critical for performance (if the struct is used in inner loops). It’s not just about safety.

See also [this explanation](https://discourse.julialang.org/t/problem-with-complex-rationals/9474/7) for why concrete fields matter.

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