# Tips for making a program more Julian

**URL:** <https://discourse.julialang.org/t/tips-for-making-a-program-more-julian/61266>\
**Category:** New to Julia\
**Tags:** question\
**Created:** [May 16, 2021, 10:57pm UTC](https://discourse.julialang.org/t/tips-for-making-a-program-more-julian/61266 "2021-05-16T22:57:12Z")\
**Posts on this page:** 6\
**Page:** 2

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**Author:** ![Vero](https://avatars.discourse-cdn.com/v4/letter/v/e19b73/32.png) [@Vero](https://discourse.julialang.org/u/Vero)\
**Post date:** [May 17, 2021, 2:26pm UTC](https://discourse.julialang.org/t/tips-for-making-a-program-more-julian/61266/21 "2021-05-17T14:26:00Z")

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Thank you for the input, I went ahead and made those changes. Would you happen to know if there is another way to create `SimOutput` through metaprogramming or something similar? Or would that just be overkill and lead to difficulties reading the code.

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**Author:** ![lmiq](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/lmiq/32/18314_2.png) [@lmiq](https://discourse.julialang.org/u/lmiq)\
**Post date:** [May 17, 2021, 2:34pm UTC](https://discourse.julialang.org/t/tips-for-making-a-program-more-julian/61266/22 "2021-05-17T14:34:51Z")

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> [@Vero](#):
>
> Or would that just be overkill and lead to difficulties reading the code.

that

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<div class="post-metadata">

**Author:** ![Vero](https://avatars.discourse-cdn.com/v4/letter/v/e19b73/32.png) [@Vero](https://discourse.julialang.org/u/Vero)\
**Post date:** [May 17, 2021, 3:03pm UTC](https://discourse.julialang.org/t/tips-for-making-a-program-more-julian/61266/23 "2021-05-17T15:03:58Z")

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I don’t think this is totally what you meant, but I made `state.y` a `Array{Float32}` and then mutated it in the `sim_prm`.

```julia
function sim_prm!(x, u, t, y, hys_state, i, output::Bool)
        # Block 3, PT1, only output
        _, y3 = pt1(x, 0)
        # Block 1, Subtractor
        y1 = -(u, y3)
        # Block 2, Hysteresis
        y2 = hysteresis(y1, hys_state, i)
        # Block 3, PT1, only state
        xdot, _ = pt1(x, y2) 
        if output
            y[1] = y1
            y[2] = y2
            y[3] = y3
        end
        return xdot
    end

```

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<div class="post-metadata">

**Author:** ![LaurentPlagne](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/laurentplagne/32/10103_2.png) [@LaurentPlagne](https://discourse.julialang.org/u/LaurentPlagne)\
**Post date:** [May 17, 2021, 3:34pm UTC](https://discourse.julialang.org/t/tips-for-making-a-program-more-julian/61266/24 "2021-05-17T15:34:04Z")

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This is ok but what is problematic with the tuple solution ?

```julia
y=ones(3)
f1() = (1,2,3)
g!(y) = y[1],y[2],y[3]=f1()
using BenchmarkTools
@benchmark g!($y)

```

cause no allocations:

```julia
BenchmarkTools.Trial: 
  memory estimate: 0 bytes
  allocs estimate: 0
  --------------
  minimum time: 1.975 ns (0.00% GC)
  median time: 1.994 ns (0.00% GC)
  mean time: 2.004 ns (0.00% GC)
  maximum time: 6.732 ns (0.00% GC)
  --------------
  samples: 10000
  evals/sample: 1000

```

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<div class="post-metadata">

**Author:** ![Vero](https://avatars.discourse-cdn.com/v4/letter/v/e19b73/32.png) [@Vero](https://discourse.julialang.org/u/Vero)\
**Post date:** [May 17, 2021, 4:06pm UTC](https://discourse.julialang.org/t/tips-for-making-a-program-more-julian/61266/25 "2021-05-17T16:06:38Z")

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Oh! I didn’t realize you could do that, as Tuples are immutable. I tried having y as a  
`Tuple{Float32}`, but I couldn’t mutate it after the initial assignment. I do like your solution more and I’ll implement it. Thank you very much for the help!

---

<div class="post-metadata">

**Author:** ![lmiq](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/lmiq/32/18314_2.png) [@lmiq](https://discourse.julialang.org/u/lmiq)\
**Post date:** [May 17, 2021, 4:32pm UTC](https://discourse.julialang.org/t/tips-for-making-a-program-more-julian/61266/26 "2021-05-17T16:32:42Z")

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Small vectors like that `y` are also the place for `StaticArrays`:

```julia
julia> using StaticArrays

julia> f() = @SVector [1,2,3]
f (generic function with 1 method)

julia> y = f()
3-element SVector{3, Int64} with indices SOneTo(3):
 1
 2
 3

julia> using BenchmarkTools

julia> @btime f()
  0.021 ns (0 allocations: 0 bytes)

```

Your structs can also be cleaner (maybe that is where you thought metaprogramming could be useful) using more extensively the `@kwdef` or, with some more features, the `Parameters` package:

```julia
julia> using Parameters

julia> @with_kw struct SimOutput{T}
         x_values::Vector{T} = Float32[]
         u_values::Vector{T} = Float32[]
       end
SimOutput

julia> SimOutput()
SimOutput{Float32}
  x_values: Array{Float32}((0,)) Float32[]
  u_values: Array{Float32}((0,)) Float32[]

julia> SimOutput{Float64}()
SimOutput{Float64}
  x_values: Array{Float64}((0,)) Float64[]
  u_values: Array{Float64}((0,)) Float64[]

julia> Out = SimOutput()
SimOutput{Float32}
  x_values: Array{Float32}((0,)) Float32[]
  u_values: Array{Float32}((0,)) Float32[]

julia> @unpack x_values, u_values = Out # can use this inside your functions
SimOutput{Float32}
  x_values: Array{Float32}((0,)) Float32[]
  u_values: Array{Float32}((0,)) Float32[]

julia> x_values
Float32[]

```

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