# Question on functions as parameters

**URL:** https://discourse.julialang.org/t/question-on-functions-as-parameters/43618
**Category:** General Usage
**Tags:** question
**Created:** [July 24, 2020, 2:22pm UTC](https://discourse.julialang.org/t/question-on-functions-as-parameters/43618 "2020-07-24T14:22:05Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![janrpeters](https://avatars.discourse-cdn.com/v4/letter/j/d26b3c/32.png) [@janrpeters](https://discourse.julialang.org/u/janrpeters)
#### Post date: [July 24, 2020, 2:22pm UTC](https://discourse.julialang.org/t/question-on-functions-as-parameters/43618/1 "2020-07-24T14:22:05Z")

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Let’s assume I would like write a function that takes functions as parameters:

```julia
function f1(f::Function)
     println("f maps from Float64 to Int64")
end

```

and I only want to allow functions

```julia
function f(x:: Float64) :: Int64
    ...
end

```

as arguments. Can I do that through the type (ie replace “::function” by something more specific)?

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<div class="post-metadata">

### Author: ![Tamas\_Papp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tamas_papp/32/25949_2.png) [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)
#### Post date: [July 24, 2020, 2:40pm UTC](https://discourse.julialang.org/t/question-on-functions-as-parameters/43618/2 "2020-07-24T14:40:59Z")

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No.

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<div class="post-metadata">

### Author: ![Oscar\_Smith](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/oscar_smith/32/25343_2.png) [@Oscar\_Smith](https://discourse.julialang.org/u/Oscar_Smith)
#### Post date: [July 24, 2020, 2:44pm UTC](https://discourse.julialang.org/t/question-on-functions-as-parameters/43618/3 "2020-07-24T14:44:17Z")

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If you have a specific set of functions you’re thinking about, you could form the union of them (since each function is it’s own type). That said, doing so will not be any faster.