# Why would you create a subtype of \`Function\`?
**URL:** https://discourse.julialang.org/t/why-would-you-create-a-subtype-of-function/77087
**Category:** General Usage
**Created:** [February 25, 2022, 5:52pm UTC](https://discourse.julialang.org/t/why-would-you-create-a-subtype-of-function/77087 "2022-02-25T17:52:29Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@nchisholm](https://discourse.julialang.org/u/nchisholm)
#### Post date: [February 25, 2022, 5:52pm UTC](https://discourse.julialang.org/t/why-would-you-create-a-subtype-of-function/77087/1 "2022-02-25T17:52:29Z")
I am curious about the utility of creating abstract or concrete subtypes of `Function`.
Aside from syntactic convenience, I am not sure of the distinction between a singleton type that is given several methods and a function definition.
```julia
struct MulPlus1T end
mulplus1 = MulPlus1T()
(::MulPlus1T)(x) = x+1
(::MulPlus1T)(x,y) = x*y+1
```
I can add as many methods as I want to `mulplus1`, so it seems to do everything a `Function` can.
Then, what utility is there to making `MyFuncType` a subtype of `<:Function`? As far as I know, it would allow `myfunc` to be used in methods of higher order functions that specifically demand that the argument `isa Function`, but I usually do not see this in practice because it would exclude user defined callable objects (which perhaps might be a subtype of some other abstract type and thus cannot be a `Function`).
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### Author:  [@jling](https://discourse.julialang.org/u/jling)
#### Post date: [February 25, 2022, 5:53pm UTC](https://discourse.julialang.org/t/why-would-you-create-a-subtype-of-function/77087/2 "2022-02-25T17:53:39Z")
there are probably two million things you can do with julia typing system that is useless.
`Function` is used for dispatching mostly, not to create subtype of directly:
```julia
julia> sin isa Function
true
```
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### Author:  [@nchisholm](https://discourse.julialang.org/u/nchisholm)
#### Post date: [February 25, 2022, 5:56pm UTC](https://discourse.julialang.org/t/why-would-you-create-a-subtype-of-function/77087/3 "2022-02-25T17:56:19Z")
Fair point, but then why have `Function` in the first place?
Is there a case where you would actually want to dispatch on `Function` and explicitly disallow user defined callable objects?
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### Author:  [@favba](https://discourse.julialang.org/u/favba)
#### Post date: [February 25, 2022, 9:58pm UTC](https://discourse.julialang.org/t/why-would-you-create-a-subtype-of-function/77087/4 "2022-02-25T21:58:03Z")
I think this is related to the good’old traits vs types discussion…
If julia had traits you would dispatch on a `Is_callable` trait. Since julia is based on types you dispatch on the `Function` type…