# Traits in Julia?
**URL:** https://discourse.julialang.org/t/traits-in-julia/17267
**Category:** General Usage
**Tags:** traits
**Created:** [November 7, 2018, 4:52pm UTC](https://discourse.julialang.org/t/traits-in-julia/17267 "2018-11-07T16:52:03Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@peter.wolf](https://discourse.julialang.org/u/peter.wolf)
#### Post date: [November 7, 2018, 4:52pm UTC](https://discourse.julialang.org/t/traits-in-julia/17267/1 "2018-11-07T16:52:03Z")
Is there an idiomatic way to do user defined traits ala Scala or Rust, or interfaces ala Java?
I want to define ‘contracts’ so I know which functions are available for my arguments. Julia has predefined interfaces such as Iteration. How does one declare new ones?
Thanks
P
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### Author:  [@StefanKarpinski](https://discourse.julialang.org/u/StefanKarpinski)
#### Post date: [November 7, 2018, 4:53pm UTC](https://discourse.julialang.org/t/traits-in-julia/17267/2 "2018-11-07T16:53:52Z")
> [@peter.wolf](#):
>
> Julia has predefined interfaces such as Iteration.
There is no first class “Iteration” concept in Julia—it’s just a convention with documentation. That’s the current approach to this sort of thing, similar to duck typing in other dynamic languages. We would like to add a first-class interface/protocol/concept entity at some point, but it was beyond the scope of the 1.0 release of the language.
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### Author:  [@peter.wolf](https://discourse.julialang.org/u/peter.wolf)
#### Post date: [November 7, 2018, 5:13pm UTC](https://discourse.julialang.org/t/traits-in-julia/17267/3 "2018-11-07T17:13:52Z")
OK, thanks. I will ‘duck’ for now and look forward to some future release
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### Author:  [@mauro3](https://discourse.julialang.org/u/mauro3)
#### Post date: [November 7, 2018, 5:19pm UTC](https://discourse.julialang.org/t/traits-in-julia/17267/4 "2018-11-07T17:19:59Z")
Also have a look at [Methods · The Julia Language](https://docs.julialang.org/en/v1/manual/methods/#Trait-based-dispatch-1)
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### Author:  [@Elrod](https://discourse.julialang.org/u/Elrod)
#### Post date: [November 7, 2018, 5:22pm UTC](https://discourse.julialang.org/t/traits-in-julia/17267/5 "2018-11-07T17:22:00Z")
You can define your own in the same way the “Iteration” or “AbstractArray” conventions are defined.
Ie, with documentation and a host of methods that will work on any type with which it is defined.
mauro3 also created the [SimpleTraits.jl](https://github.com/mauro3/SimpleTraits.jl) library.