# Runtime dispatch in struct that contains struct
**URL:** https://discourse.julialang.org/t/runtime-dispatch-in-struct-that-contains-struct/118840
**Category:** New to Julia
**Tags:** runtime-dispatch
**Created:** [August 31, 2024, 12:02pm UTC](https://discourse.julialang.org/t/runtime-dispatch-in-struct-that-contains-struct/118840 "2024-08-31T12:02:43Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@JADekker](https://discourse.julialang.org/u/JADekker)
#### Post date: [August 31, 2024, 12:02pm UTC](https://discourse.julialang.org/t/runtime-dispatch-in-struct-that-contains-struct/118840/1 "2024-08-31T12:02:43Z")
Hi, in my code, I have a structure similar to the below. The function that I call in `running` should be determined by `FooContainer.foo`, so it is clear to me that I have runtime dispatch here. What is the idiomatic way to work around this runtime dispatch here? I would guess that using one method for `run_foo` in which I check the type of `foo`, e.g. using `isa(foo, Foo1)` resolves the problem, but is this the preferred solution? In reality, I’ll have a few (5-10) subtypes of `FooType` and would like to dispatch on `x`, which may have various types (say vector, matrix, float etc.), so I want to make sure that I get the right approach here…
```julia
using JET
abstract type FooType end
struct Foo1 <: FooType end
struct Foo2 <: FooType end
struct FooContainer
foo::FooType
end
function run_foo(foo::Foo1, x::Float64)
return x
end
function run_foo(foo::Foo2, x::Float64)
return x^2
end
function running(foo_container::FooContainer, x::Float64)
return run_foo(foo_container.foo, x)
end
rep = @report_opt running(FooContainer(Foo1()), 2.0)
show(rep)
```
which returns
```julia
═════ 1 possible error found ═════
┌ running(foo_container::FooContainer, x::Float64) @ (HIDDEN)
│ runtime dispatch detected: run_foo(%1::FooType, x::Float64)::Float64
```
---
### Author:  [@Tarny\_GG\_Channie](https://discourse.julialang.org/u/Tarny_GG_Channie)
#### Post date: [August 31, 2024, 1:50pm UTC](https://discourse.julialang.org/t/runtime-dispatch-in-struct-that-contains-struct/118840/2 "2024-08-31T13:50:36Z")
> [@JADekker](#):
>
> ```julia
> struct FooContainer
> foo::FooType
> end
>
> ```
Here.
You need to fully parameterize the FooContainer type. As of now, the FooContainer type can hold any type that is of FooType as foo.
---
### Author:  [@stevengj](https://discourse.julialang.org/u/stevengj)
#### Post date: [August 31, 2024, 1:56pm UTC](https://discourse.julialang.org/t/runtime-dispatch-in-struct-that-contains-struct/118840/3 "2024-08-31T13:56:52Z")
See the [performance tips: avoid fields with abstract type](https://docs.julialang.org/en/v1/manual/performance-tips/#Avoid-fields-with-abstract-type).
---
### Author:  [@JADekker](https://discourse.julialang.org/u/JADekker)
#### Post date: [August 31, 2024, 2:05pm UTC](https://discourse.julialang.org/t/runtime-dispatch-in-struct-that-contains-struct/118840/4 "2024-08-31T14:05:48Z")
I see, thank you! So if I simply parametrise the type here, I should be fine? That would be very nice! I’ll check once I have time and mark this as the solution afterwards!
Is there some tooling that automatically identifies such issues? (under-parametrised types?)
---
### Author:  [@stevengj](https://discourse.julialang.org/u/stevengj)
#### Post date: [August 31, 2024, 2:18pm UTC](https://discourse.julialang.org/t/runtime-dispatch-in-struct-that-contains-struct/118840/5 "2024-08-31T14:18:38Z")
> [@JADekker](#):
>
> So if I simply parametrise the type here, I should be fine?
Yes.
---
### Author:  [@Mason](https://discourse.julialang.org/u/Mason)
#### Post date: [August 31, 2024, 2:33pm UTC](https://discourse.julialang.org/t/runtime-dispatch-in-struct-that-contains-struct/118840/6 "2024-08-31T14:33:34Z")
It really depends. Generally speaking, you’ll probably want
> [@stevengj](#):
>
> > [@JADekker](#):
> >
> > So if I simply parametrise the type here, I should be fine?
>
> Yes.
Just to expand on this, you’ll only be okay if the compiler can know ahead of time what the parameter is.
For example, if you have a vector with `FooContainer`s that have many different `FooType`s inside of them, then paramerizing wont help at all.
In cases like that, I would instead recommend an approach like [SumTypes.jl](https://github.com/MasonProtter/SumTypes.jl) or Moshi.jl.
These packages specialize in taking situations where you have a finite number of options and writing code that handles each of those options in a more efficient way than dispatch can. There’s tradeoffs like a lack of extensibility, but the advantages can be quite nice too.