# Type instability if I map over array of functions

**URL:** https://discourse.julialang.org/t/type-instability-if-i-map-over-array-of-functions/12817
**Category:** General Usage
**Created:** [August 2, 2018, 10:32am UTC](https://discourse.julialang.org/t/type-instability-if-i-map-over-array-of-functions/12817 "2018-08-02T10:32:25Z")
**Posts on this page:** 2
**Page:** 1

<div class="post-metadata">

### Author: ![zsoerenm](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/zsoerenm/32/664_2.png) [@zsoerenm](https://discourse.julialang.org/u/zsoerenm)
#### Post date: [August 2, 2018, 10:32am UTC](https://discourse.julialang.org/t/type-instability-if-i-map-over-array-of-functions/12817/1 "2018-08-02T10:32:25Z")

</div>

Hello,

when I map over an array of functions, the ouput is type unstable.

Minimal example:

```julia
struct StructA
    val::Float64
end
struct StructB
    val::Float64
end
function init_add(struct_a::StructA)
    y -> struct_a.val + y + 0.1
end
function init_add(struct_b::StructB)
    y -> struct_b.val + y + 0.2
end
A = [init_add(StructA(1.1)), init_add(StructB(2.2))]
@code_warntype map(a -> a(0.1), A)

```

Output:

```julia
Variables:
  #self# <optimized out>
  f <optimized out>
  A::Array{Function,1}

Body:
  begin 
      return $(Expr(:invoke, MethodInstance for _collect(::Array{Function,1}, ::Base.Generator{Array{Function,1},##5#6}, ::Base.EltypeUnknown, ::Base.HasShape), :(Base._collect), :(A), :($(Expr(:new, Base.Generator{Array{Function,1},##5#6}, :($(QuoteNode(#5))), :(A)))), :($(QuoteNode(Base.EltypeUnknown()))), :($(QuoteNode(Base.HasShape())))))
  end::Array{_,1} where _

```

where `Array{_,1} where _` is red.

This could easily be fixed by doing:

```julia
map(a -> a(0.1)::Float64, A)

```

but unfortunately I need to return Tuple with an anonymous function:

```julia
map(a -> (b -> a(b), a(0.1)), A)

```

Is there still a Trick to get this type stable?

---

<div class="post-metadata">

### Author: ![tkoolen](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tkoolen/32/1603_2.png) [@tkoolen](https://discourse.julialang.org/u/tkoolen)
#### Post date: [August 2, 2018, 10:43am UTC](https://discourse.julialang.org/t/type-instability-if-i-map-over-array-of-functions/12817/2 "2018-08-02T10:43:54Z")

</div>

`Function` is an abstract type. Look at

```julia
julia> typeof(init_add(StructA(1.1)))
##3#4{StructA}

julia> typeof(init_add(StructB(2.2)))
##5#6{StructB}

```

Since these types are different, iterating over a `Vector` containing elements of both types is the same as iterating over any other type-heterogeneous collection (e.g. `Number[1, 2.0]`). See [this post](https://discourse.julialang.org/t/is-there-a-way-to-forward-getindex-for-tuples-in-a-type-stable-way/2889/20) for example for some options.