# Type instability with StaticArrays
**URL:** https://discourse.julialang.org/t/type-instability-with-staticarrays/20084
**Category:** New to Julia
**Tags:** question
**Created:** [January 25, 2019, 11:32am UTC](https://discourse.julialang.org/t/type-instability-with-staticarrays/20084 "2019-01-25T11:32:01Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@bachrathyd](https://discourse.julialang.org/u/bachrathyd)
#### Post date: [January 25, 2019, 11:32am UTC](https://discourse.julialang.org/t/type-instability-with-staticarrays/20084/1 "2019-01-25T11:32:01Z")
Hi all,
I was unable to create a type stable static matrix from an Array{T,2}
How make it type stable?
Tanks!
```julia
using StaticArrays
function Tmaker(kdim::IT) where IT<:Integer
T=reshape([isodd(x÷(2^y)) for y in 0:(kdim-1) for x in 0:(2^kdim-1)],:,kdim)
TT=SMatrix{size(T)...}(T)
end
@code_warntype Tmaker(3)
```
---
### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [January 25, 2019, 11:38am UTC](https://discourse.julialang.org/t/type-instability-with-staticarrays/20084/2 "2019-01-25T11:38:53Z")
> [@bachrathyd](#):
>
> I was unable to create a type stable static matrix from an Array{T,2}
Yes, you are unable to do that. `Array{T,2}` has insufficient type information to be able to specify a fully typed static array at compile time.
---
### Author:  [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [January 25, 2019, 11:39am UTC](https://discourse.julialang.org/t/type-instability-with-staticarrays/20084/3 "2019-01-25T11:39:36Z")
This is inherently type unstable in that the type of the output depends on the value of the input.
You can give the input as a type and do something like
```julia
function Tmaker(::Val{kdim}) where {kdim}
T=reshape([isodd(x÷(2^y)) for y in 0:(kdim-1) for x in 0:(2^kdim-1)],:,kdim)
TT=SMatrix{2^kdim, kdim}(T)
end
```
```julia
julia> @code_warntype Tmaker(Val(2))
Body::SArray{Tuple{4,2},Bool,2,8}
```
or you just work around the type instability using a function barrier (see performance tips in the julia manual).
---
### Author:  [@improbable22](https://discourse.julialang.org/u/improbable22)
#### Post date: [January 25, 2019, 11:53am UTC](https://discourse.julialang.org/t/type-instability-with-staticarrays/20084/4 "2019-01-25T11:53:07Z")
> [@kristoffer.carlsson](#):
>
> julia\> @code\_warntype Tmaker(Val(2)) Body::SArray{Tuple{4,2},Bool,2,8}
That’s interesting, I tried exactly the same value type trick, but tested with `kdim=3` and saw that it wasn’t type-stable, because `SMatrix{2^kdim, kdim}` has a calculation:
```julia
@code_warntype Tmaker(Val(3))
```
Somehow 2^2 is caught as a special case that can be inferred?
---
### Author:  [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [January 25, 2019, 12:01pm UTC](https://discourse.julialang.org/t/type-instability-with-staticarrays/20084/5 "2019-01-25T12:01:41Z")
Ah, the `^2` is special cased. Can hack around it with:
```julia
julia> Base.@pure mypow(x, y) = x^y
mypow (generic function with 1 method)
julia> function Tmaker(::Val{kdim}) where {kdim}
T=reshape([isodd(x÷(2^y)) for y in 0:(kdim-1) for x in 0:(2^kdim-1)],:,kdim)
TT=SMatrix{mypow(kdim, 2), kdim}(T)
end
Tmaker (generic function with 2 methods)
julia> @code_warntype Tmaker(Val(3))
Body::SArray{Tuple{9,3},Bool,2,27}
```
---
### Author:  [@improbable22](https://discourse.julialang.org/u/improbable22)
#### Post date: [January 25, 2019, 12:16pm UTC](https://discourse.julialang.org/t/type-instability-with-staticarrays/20084/6 "2019-01-25T12:16:21Z")
Nice. I’m terrified of `@pure` but was cobbling this together:
```julia
@generated twopow(::Val{n}) where n = 2^n
function Tmaker(valk::Val{kdim}) where {kdim}
M=reshape([isodd(x÷(2^y)) for y in 0:(kdim-1) for x in 0:(2^kdim-1)],:,kdim)
SMatrix{twopow(valk), kdim}(M)
end
@code_warntype Tmaker(Val(3))
```
---
### Author:  [@bachrathyd](https://discourse.julialang.org/u/bachrathyd)
#### Post date: [January 25, 2019, 1:27pm UTC](https://discourse.julialang.org/t/type-instability-with-staticarrays/20084/7 "2019-01-25T13:27:28Z")
Thank you for your fast help!