# Help to remove type instability
**URL:** https://discourse.julialang.org/t/help-to-remove-type-instability/37988
**Category:** General Usage
**Created:** [April 21, 2020, 7:17pm UTC](https://discourse.julialang.org/t/help-to-remove-type-instability/37988 "2020-04-21T19:17:57Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@Ronis\_BR](https://discourse.julialang.org/u/Ronis_BR)
#### Post date: [April 21, 2020, 7:17pm UTC](https://discourse.julialang.org/t/help-to-remove-type-instability/37988/1 "2020-04-21T19:17:57Z")
Hi!
I am trying to create a signal system for my package [TextUserInterfaces.jl](https://github.com/ronisbr/TextUserInterfaces.jl).
As of now, I have the following kind of structure defining a signal that will be emitted when return is pressed:
```julia
mutable struct Object
on_return_pressed::Function
vargs_on_return_pressed::Tuple
end
```
Then, the user can connect a function to be executed with this signal using:
```julia
obj = Object( ()->nothing, tuple() )
func(a,b) = a+b
obj.on_return_pressed = func
obj.vargs_on_return_pressed = (1,2)
```
It is working fine. The problem is that when I call `on_return_pressed` I have a type instability. Can anyone help me to remove it? See the following MWE:
```julia
julia> mutable struct Object
on_return_pressed::Function
vargs_on_return_pressed::Tuple
end
julia> function test()
obj = Object( ()->nothing, tuple() )
func(a,b) = a+b
obj.on_return_pressed = func
obj.vargs_on_return_pressed = (1,2)
return obj.on_return_pressed(obj.vargs_on_return_pressed...)
end
test (generic function with 1 method)
julia> @code_warntype test()
Variables
#self#::Core.Compiler.Const(test, false)
#3::var"#3#4"
obj::Object
func::var"#func#5"
Body::Any
1 ─ (#3 = %new(Main.:(var"#3#4")))
│ %2 = #3::Core.Compiler.Const(var"#3#4"(), false)
│ %3 = Main.tuple()::Core.Compiler.Const((), false)
│ (obj = Main.Object(%2, %3))
│ (func = %new(Main.:(var"#func#5")))
│ Base.setproperty!(obj, :on_return_pressed, func)
│ %7 = Core.tuple(1, 2)::Core.Compiler.Const((1, 2), false)
│ Base.setproperty!(obj, :vargs_on_return_pressed, %7)
│ %9 = Base.getproperty(obj, :on_return_pressed)::Function
│ %10 = Base.getproperty(obj, :vargs_on_return_pressed)::Tuple
│ %11 = Core._apply_iterate(Base.iterate, %9, %10)::Any
└── return %11
```
---
### Author:  [@mauro3](https://discourse.julialang.org/u/mauro3)
#### Post date: [April 21, 2020, 7:21pm UTC](https://discourse.julialang.org/t/help-to-remove-type-instability/37988/2 "2020-04-21T19:21:40Z")
You probably need to use a type parameter for the field holding the function as `Function` is abstract. Same goes for Tuple:
```julia
mutable struct Object{F<:Function, T<:Tuple}
on_return_pressed::F
vargs_on_return_pressed::T
end
```
Edit: But note, that with this approach compile time will go up as new JITting needs to happen for all different `F` and `T`. This application seems like it might be better off with a type-instability.
---
### Author:  [@Ronis\_BR](https://discourse.julialang.org/u/Ronis_BR)
#### Post date: [April 21, 2020, 7:29pm UTC](https://discourse.julialang.org/t/help-to-remove-type-instability/37988/3 "2020-04-21T19:29:37Z")
Thanks! The other problem is that the user will need to have the signal function ready when the object is created. I think I can add a macro to annotate the function with the return type in case the user wants type instability.
---
### Author:  [@Oscar\_Smith](https://discourse.julialang.org/u/Oscar_Smith)
#### Post date: [April 21, 2020, 7:39pm UTC](https://discourse.julialang.org/t/help-to-remove-type-instability/37988/4 "2020-04-21T19:39:09Z")
A halfway measure would be to only specialize the `Object` on function type, as this is probably more important.
---
### Author:  [@Ronis\_BR](https://discourse.julialang.org/u/Ronis_BR)
#### Post date: [April 21, 2020, 7:46pm UTC](https://discourse.julialang.org/t/help-to-remove-type-instability/37988/5 "2020-04-21T19:46:17Z")
But, in this case, the user will not be able to change the signal (the function) after the object is created, right?
---
### Author:  [@Oscar\_Smith](https://discourse.julialang.org/u/Oscar_Smith)
#### Post date: [April 21, 2020, 7:48pm UTC](https://discourse.julialang.org/t/help-to-remove-type-instability/37988/6 "2020-04-21T19:48:29Z")
Correct.