# Simple type problem
**URL:** https://discourse.julialang.org/t/simple-type-problem/70958
**Category:** Performance
**Tags:** structtypes
**Created:** [November 4, 2021, 2:45pm UTC](https://discourse.julialang.org/t/simple-type-problem/70958 "2021-11-04T14:45:39Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Igor\_Douven](https://discourse.julialang.org/u/Igor_Douven)
#### Post date: [November 4, 2021, 2:45pm UTC](https://discourse.julialang.org/t/simple-type-problem/70958/1 "2021-11-04T14:45:39Z")
I have an abstract type,
```julia
abstract type AT end
```
and two `mutable struct`s that are subtypes of `AT`:
```julia
mutable struct S1 <: AT
#something
end
mutable struct S2 <: AT
#something
end
```
I would like to define a function that takes as argument vectors that can contain either `S1`s or `S2`s or both. I had hoped that the following would work:
```julia
function fnc(v::Vector{AT})
#something
end
```
However, it turns out that it works only if the vector contains **both** `S1`s and `S2`s. If, for instance, the argument is a `Vector{S1}` the function throws an error. I’m sure there is a simple solution but I can’t think of it. Help would be much appreciated.
---
### Author:  [@stillyslalom](https://discourse.julialang.org/u/stillyslalom)
#### Post date: [November 4, 2021, 2:51pm UTC](https://discourse.julialang.org/t/simple-type-problem/70958/2 "2021-11-04T14:51:16Z")
You’ll want to specify a subtype `<:` relationship for the elements of the vector:
```julia
function fnc(v::Vector{<:AT})
```
---
### Author:  [@Igor\_Douven](https://discourse.julialang.org/u/Igor_Douven)
#### Post date: [November 4, 2021, 3:07pm UTC](https://discourse.julialang.org/t/simple-type-problem/70958/3 "2021-11-04T15:07:08Z")
Perfect! Thank you very much.