# How to specify the type of a Tracked CuArray?

**URL:** <https://discourse.julialang.org/t/how-to-specify-the-type-of-a-tracked-cuarray/25406>\
**Category:** Performance\
**Created:** [June 18, 2019, 12:37pm UTC](https://discourse.julialang.org/t/how-to-specify-the-type-of-a-tracked-cuarray/25406 "2019-06-18T12:37:41Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![HenriDeh](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/henrideh/32/8316_2.png) [@HenriDeh](https://discourse.julialang.org/u/HenriDeh)\
**Post date:** [June 18, 2019, 12:37pm UTC](https://discourse.julialang.org/t/how-to-specify-the-type-of-a-tracked-cuarray/25406/1 "2019-06-18T12:37:41Z")

</div>

Hello,

I have a function that calls neural networks on the gpu and I would like to specify the return type for performances.

```julia
using Flux
net = Chain(Dense(3,2,relu)) |> gpu
function foo(net::Chain, input::CuArray{Float32})::TrackedArray
    net(input)
end

out = foo(net, cu([1f0,1f0,1f0]))
typeof(out)
> TrackedArray{...,CuArray{Float32,1}}

```

I would like to specify that `::TrackedArray{...,CuArray{Float32,1}}` instead of simply `TrackedArray` but with the `...,` returns syntax: invalid identifier name “…”. If I use `::TrackedArray{CuArray{Float32,1}}` instead it compiles but it throws a convert error:

```julia
ERROR: Not implemented: convert TrackedArray{…,CuArray{Float32,1}} to TrackedArray{CuArray{Float32,1},N,A} where A<:AbstractArray{CuArray{Float32,1},N} where N

```

I think it’s important for performance that the compiler know that the TrackedArray is in the GPU, correct me if I’m wrong, I’m just assuming.