# Julia is Overwriting output of a Function

**URL:** <https://discourse.julialang.org/t/julia-is-overwriting-output-of-a-function/68061>\
**Category:** General Usage\
**Tags:** question\
**Created:** [September 12, 2021, 8:20pm UTC](https://discourse.julialang.org/t/julia-is-overwriting-output-of-a-function/68061 "2021-09-12T20:20:35Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![jmcastro2109](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jmcastro2109/32/38427_2.png) [@jmcastro2109](https://discourse.julialang.org/u/jmcastro2109)\
**Post date:** [September 12, 2021, 8:20pm UTC](https://discourse.julialang.org/t/julia-is-overwriting-output-of-a-function/68061/1 "2021-09-12T20:20:35Z")

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Hello,

I am having a very weird behavior in Julia, however, I am having a hard time reproducing it in a MWE. Let me try to describe it, with an example which does not reproduce the error

```julia
function test(x,y)

        results = 0.0

        results = x+y

        return results

    end 

    Result_1 = test(1,2)

    Result_2 = test(1,7)

```

After doing this, `Result_1 == Result_2` is `true`. As I was saying this function does not reproduce the error, however, it captures the idea of what is happening in the actual problematic function. I run it with two different inputs, and the second run overwrites the value of the first run.

This is the function where this is happening. Could this possibly be related with the SharedArrays ?

```julia

	function counterfactuals_generator(ZSeeds_cf,FSeeds_cf,ProbsSeeds,seeds_climate_cf,β,α,τ,J,Ι,S,Simul,N,params)
		(κ,σ,σ₁,σ₂,χ)=params
		κt = (κ)^(1/σ)
		μ = params[6:end]
		println(1000000 .*μ)
		ftemp = σ₁.*FSeeds_cf .+ 1000000 .*μ.*ones(size(FSeeds_cf))
		F = exp.(ftemp)
		#F = zeros(size(F))

		κᵢ = κt.*(seeds_climate_cf .< ProbsSeeds)
		κᵢ[κᵢ .== 0.0] .= 1.0

		ztemp = σ₂*ZSeeds_cf .+ 0.0.*ones(size(ZSeeds_cf))
		Z = exp.(ztemp)

		taus = exp.(τ).^(-1/σ)
		

		Random.seed!(0607)
		ParetoDraws = rand(Pareto(χ,0.783),N)

		ϕ(φ) = φ^(σ-1)*(σ/(σ-1))^(1-σ)*1/σ

		FirmShifters = ϕ.(ParetoDraws)
		println("Computing Marginal Costs")
		mc_simul=marginalcost_cf(κᵢ,Z,α,taus,Ι,J,S,N,Simul)
		solution=SharedArray{Int8}(Ι,N,Simul)
		policies=SharedArray{Int8}(Ι,J,S,N,Simul)
		profit=SharedArray{Float64}(N,Simul)
		
		println("Pre-Stuff Done")
		for s = 1 : Simul
			println(s)
			@sync @distributed for n=1:N
			#println("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Firm # %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%: ", n)
			sol = firmproblem(mc_simul[:,:,:,n,s],σ,F[:,n,s],J,Ι,S,κ,FirmShifters[n],β)
			solution[:,n,s]= sol[1]
			policies[:,:,:,n,s]=sol[2]
			profit[n,s] = sol[3]
			#println("%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Firm # %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%: ", n)
			end
		end
		return solution, policies, FirmShifters, F, κᵢ, mc_simul, profit
	end		

```

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<div class="post-metadata">

**Author:** ![jmcastro2109](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jmcastro2109/32/38427_2.png) [@jmcastro2109](https://discourse.julialang.org/u/jmcastro2109)\
**Post date:** [September 12, 2021, 8:29pm UTC](https://discourse.julialang.org/t/julia-is-overwriting-output-of-a-function/68061/2 "2021-09-12T20:29:19Z")

</div>

Seems that returning a copy of solution, policies and profit solves the issue. Interesting, because it seems that this does not happen all the time.

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<div class="post-metadata">

**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:** [September 13, 2021, 5:13am UTC](https://discourse.julialang.org/t/julia-is-overwriting-output-of-a-function/68061/3 "2021-09-13T05:13:09Z")

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You have probably been bitten by

```julia
julia> a = [1]
1-element Vector{Int64}:
 1

julia> b = a
1-element Vector{Int64}:
 1

julia> b[1] = 2
2

julia> a
1-element Vector{Int64}:
 2

```

the line `b = a` will just assign a new _name_ `b` to the data that is referenced by `a`, and both `b` and `a` will point to the same memory. Returning a `copy` thus solves the problem since the memory is then copied and they no longer reference the same.