# I need some help defining an interface that would kind of be a static class method

**URL:** <https://discourse.julialang.org/t/i-need-some-help-defining-an-interface-that-would-kind-of-be-a-static-class-method/54883>\
**Category:** General Usage\
**Created:** [February 9, 2021, 12:20am UTC](https://discourse.julialang.org/t/i-need-some-help-defining-an-interface-that-would-kind-of-be-a-static-class-method/54883 "2021-02-09T00:20:49Z")\
**Posts on this page:** 2\
**Page:** 1

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**Post date:** [February 9, 2021, 12:20am UTC](https://discourse.julialang.org/t/i-need-some-help-defining-an-interface-that-would-kind-of-be-a-static-class-method/54883/1 "2021-02-09T00:20:49Z")

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I need some help defining an interface that would kind of be a static class method in an OO language (while also having concrete instances of the contextual class with functionality in the class methods). For simplicity, let’s say I have a method, some context-defining types like `Parabola` or `Line` and a function like `evaluate` where I want to define evaluate with something like this `evaluate(Parabola, coefs::Vector{Number}, x::Number}) = coefs[1] * x^2 + coefs[2] * x + coefs[3]` and `evaluate(Line, coefs::Vector{Number}, x::Number) = coefs[1] * x + coefs[2]`. I know this can easily be solved in this particular case another way, but it’s just an example of the behavior.

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**Author:** ![JHonaker](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jhonaker/32/18558_2.png) [@JHonaker](https://discourse.julialang.org/u/JHonaker)\
**Post date:** [February 16, 2021, 4:18pm UTC](https://discourse.julialang.org/t/i-need-some-help-defining-an-interface-that-would-kind-of-be-a-static-class-method/54883/2 "2021-02-16T16:18:37Z")

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Unsurprisingly, this is definitely supported. It was pointed out to me that this is exactly how the fitting procedures in `Distributions.jl` work.

The needed function signature would be something like:

```julia
evaluate(::Type{Parabola}, coefs::Vector{<:Number}, x::Number) = ...

# or 

evaluate(::Type{Line}, coefs::Vector{<:Number}, x::Number) = ...

```