# Function wrapper with parameterse from struct

**URL:** <https://discourse.julialang.org/t/function-wrapper-with-parameterse-from-struct/44794>\
**Category:** General Usage\
**Tags:** question\
**Created:** [August 12, 2020, 9:27am UTC](https://discourse.julialang.org/t/function-wrapper-with-parameterse-from-struct/44794 "2020-08-12T09:27:03Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Znerual](https://avatars.discourse-cdn.com/v4/letter/z/6de8d8/32.png) [@Znerual](https://discourse.julialang.org/u/Znerual)\
**Post date:** [August 12, 2020, 9:27am UTC](https://discourse.julialang.org/t/function-wrapper-with-parameterse-from-struct/44794/1 "2020-08-12T09:27:03Z")

</div>

Dear all,  
I’m trying to figure out how to nicely wrap my function into a struct (or possible other type), which holds all the parameters I want to set before the function is called.  
The idea around that is that I’m passing an array of this struct into another function which should than only care about one argument of the function. This other function expects:

```julia
Array{Function,1}

```

My first idea was to just wrap-up the function with another function like this:

```julia
function spin_up3(psi::Union{Array{Complex{Float64},1},Array{Float64,1}})::Function
        number_operator!(H::Hubbard, psi, 1,1)
    end

```

and than fill the array with spin\_up3 and similar functions. That worked fine until I used an array of length 1

```julia
[spin_up3]

```

when Julia didn’t recognice the Type as Function but as typeof{spin\_up3} and threw me a typeassert error because typeof{spin\_up3} didn’t seem to be a Function.

What I would like to have is something like that,

```julia
struct SpinOperator <: Operator
    state::Int
    sigma::Int
   

    act = function act(psi::Union{Array{Complex{Float64},1},Array{Float64,1}})::Function
        number_operator!(H::Hubbard, psi, state,sigma)
    end
    SpinOperator(state::Int, sigma::Int) = new(state, sigma)
end

```

which calls the Function defined for act with the parameters state and sigma, which are set when the struct is created  
When I try to run the current code I get a LoadError because he complains that he doesn’t have the field act.

I would really appreceate your help on that!

---

<div class="post-metadata">

**Author:** ![MatFi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/matfi/32/10002_2.png) [@MatFi](https://discourse.julialang.org/u/MatFi)\
**Post date:** [August 12, 2020, 11:03am UTC](https://discourse.julialang.org/t/function-wrapper-with-parameterse-from-struct/44794/2 "2020-08-12T11:03:20Z")

</div>

You can make the Struct callable it self:

```julia
struct SpinOperator <: Operator
    state::Int
    sigma::Int
    SpinOperator(state::Int, sigma::Int) = new(state, sigma)
end

function (act::SpinOperator)(psi::Union{Array{Complex{Float64},1},Array{Float64,1}})
        number_operator!(H::Hubbard, psi, act.state, act.sigma)# EDIT: typo
end

# Use it like this
function foo(s::SpinOperator)
   return s([42])
end

```

---

<div class="post-metadata">

**Author:** ![pbayer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pbayer/32/11675_2.png) [@pbayer](https://discourse.julialang.org/u/pbayer)\
**Post date:** [August 12, 2020, 11:09am UTC](https://discourse.julialang.org/t/function-wrapper-with-parameterse-from-struct/44794/3 "2020-08-12T11:09:59Z")

</div>

You could always (for your first approach) have a function like

```julia
function fArray(fs...)
    A = Array{Function,1}()
    for f in fs
       push!(A, f)
    end
   return A
end

```

then:

```julia
julia> fArray(sin, cos, tan)
3-element Array{Function,1}:
 sin (generic function with 13 methods)
 cos (generic function with 13 methods)
 tan (generic function with 12 methods)

julia> fArray(sin)
1-element Array{Function,1}:
 sin (generic function with 13 methods)

```