# Why Val{...}?
**URL:** https://discourse.julialang.org/t/why-val/16035
**Category:** General Usage
**Tags:** question
**Created:** [October 8, 2018, 6:19pm UTC](https://discourse.julialang.org/t/why-val/16035 "2018-10-08T18:19:37Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@e3c6](https://discourse.julialang.org/u/e3c6)
#### Post date: [October 8, 2018, 6:19pm UTC](https://discourse.julialang.org/t/why-val/16035/1 "2018-10-08T18:19:37Z")
Why is `Val{..}` needed? Shouldn’t constant propagation make `Val` obsolete ([https://github.com/JuliaLang/julia/pull/24362](https://github.com/JuliaLang/julia/pull/24362))?
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### Author:  [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [October 8, 2018, 6:43pm UTC](https://discourse.julialang.org/t/why-val/16035/3 "2018-10-08T18:43:31Z")
`Val` forces specialization which can sometimes be desired.
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### Author:  [@StefanKarpinski](https://discourse.julialang.org/u/StefanKarpinski)
#### Post date: [October 8, 2018, 6:55pm UTC](https://discourse.julialang.org/t/why-val/16035/4 "2018-10-08T18:55:57Z")
`Val` also predates that kind of contant propagation.
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### Author:  [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [October 8, 2018, 7:11pm UTC](https://discourse.julialang.org/t/why-val/16035/5 "2018-10-08T19:11:50Z")
> [@StefanKarpinski](#):
>
> `Val` also predates that kind of contant propagation.
Sure, my point was just that even now, there are reasons why it is still useful.
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### Author:  [@e3c6](https://discourse.julialang.org/u/e3c6)
#### Post date: [October 8, 2018, 7:13pm UTC](https://discourse.julialang.org/t/why-val/16035/6 "2018-10-08T19:13:15Z")
Is there an example, where constant propagation is not enough?
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### Author:  [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [October 8, 2018, 7:15pm UTC](https://discourse.julialang.org/t/why-val/16035/7 "2018-10-08T19:15:10Z")
> [@e3c6](#):
>
> Is there an example, where constant propagation is not enough?
You might not only want to specialize on constants.
> [@Getproperty, decorations, inheritance in 0.7](https://discourse.julialang.org/t/getproperty-decorations-inheritance-in-0-7/11237/14):
>
> How about if I want to dynamically specialise on a certain value? using StaticArrays function f(n::Int) b = rand(SVector{n}) for i in 1:10000 b += rand(SVector{n}) end return b end function f(\_n::Val{n}) where n b = rand(SVector{n}) for i in 1:10000 b += rand(SVector{n}) end return b end g1() = f(rand(4:4)) g2() = f(Val(rand(4:4))) @time g1() @time g2() julia\> @time g1(); 0.015060 seconds (140.02 k allocations: 8.851 MiB) julia\> @time g2(…