# On types of functions
**URL:** https://discourse.julialang.org/t/on-types-of-functions/66058
**Category:** General Usage
**Created:** [August 9, 2021, 6:22am UTC](https://discourse.julialang.org/t/on-types-of-functions/66058 "2021-08-09T06:22:40Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Judd](https://discourse.julialang.org/u/Judd)
#### Post date: [August 9, 2021, 6:22am UTC](https://discourse.julialang.org/t/on-types-of-functions/66058/1 "2021-08-09T06:22:41Z")
I propose to add a subsection “Type of Functions” to Manual / Types. This will be very helpful, especially for newcomers to learn the essentials of Julia types and functions. If anything wrong, please correct me.
> ## Types of Functions
>
> Each function has its own type, which is both concrete and singleton, and with Function as its supertype.
>
> Recall that a function is consisted by one or more methods, therefore, a function could not have a similar type signature as in other programming languages, such as C, Haskell, etc.
---
### Author:  [@jzr](https://discourse.julialang.org/u/jzr)
#### Post date: [August 9, 2021, 6:29am UTC](https://discourse.julialang.org/t/on-types-of-functions/66058/2 "2021-08-09T06:29:53Z")
You can actually have a function with no methods
```julia
julia> function foo end
foo (generic function with 0 methods)
```
but you can also specify signatures in Julia. A single syntax can create both a function and a method:
```julia
julia> (double(x::Integer)::Integer) = 2x
double (generic function with 1 method)
```
but that signature isn’t included in the type of the function, as you say. Though there have been discussions about whether it should. I personally would like to have a way of expressing the type of a function that takes Integer to Integer without specifying which particular function it is.
---
### Author:  [@Judd](https://discourse.julialang.org/u/Judd)
#### Post date: [August 9, 2021, 6:39am UTC](https://discourse.julialang.org/t/on-types-of-functions/66058/3 "2021-08-09T06:39:39Z")
Thanks. A revised version:
> ## Types of Functions
>
> Each function has its own type, which is both concrete and singleton, and with Function as its supertype.
>
> Recall that a function is consisted by methods, therefore, a function can not have a similar type signature as in other programming languages, while a method can.
---
### Author:  [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)
#### Post date: [August 10, 2021, 11:58am UTC](https://discourse.julialang.org/t/on-types-of-functions/66058/4 "2021-08-10T11:58:28Z")
Thanks for bringing up this issue, I made a PR for the docs:
[https://github.com/JuliaLang/julia/pull/41855](https://github.com/JuliaLang/julia/pull/41855)
(Incidentally, note that anonymous functions may not be singletons, I added an example).