# What is the splatting penalty?

**URL:** <https://discourse.julialang.org/t/what-is-the-splatting-penalty/32646>\
**Category:** New to Julia\
**Created:** [December 24, 2019, 6:16am UTC](https://discourse.julialang.org/t/what-is-the-splatting-penalty/32646 "2019-12-24T06:16:53Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![yuxi.liu](https://avatars.discourse-cdn.com/v4/letter/y/839c29/32.png) [@yuxi.liu](https://discourse.julialang.org/u/yuxi.liu)\
**Post date:** [December 24, 2019, 6:16am UTC](https://discourse.julialang.org/t/what-is-the-splatting-penalty/32646/1 "2019-12-24T06:16:53Z")

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I know what “splatting” is, but what is the “splatting penalty”, as seen [here](https://fluxml.ai/Flux.jl/stable/performance/#Evaluate-batches-as-Matrices-of-features,-rather-than-sequences-of-Vector-features-1)?

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**Author:** ![baggepinnen](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/baggepinnen/32/693_2.png) [@baggepinnen](https://discourse.julialang.org/u/baggepinnen)\
**Post date:** [December 24, 2019, 6:58am UTC](https://discourse.julialang.org/t/what-is-the-splatting-penalty/32646/2 "2019-12-24T06:58:06Z")

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The compiler will have to compile a new method of hcat every time the length of xs changes. That applies for the adjoint as well.