Pluto.jl - How do I dispatch to a subtype created in a notebook?

General Usage
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1

I created a small package called ProblematicAnimals.jl to demonstrate a problem I’m having with Pluto.jl notebooks. I sincerely hope a solution to this can be found.

Defined outside of Pluto

abstract type AbstractAnimal end
struct Cat <: AbstractAnimal end
sound(cat::Cat) = "meow"
why(a::AbstractAnimal) = sound(a)

It should work like this.

julia> cat = Cat()
Cat()

julia> sound(cat)
"meow"

julia> why(cat)
"meow"

Simple.

However, I can’t get a subtype defined in a notebook to work.

From inside Pluto.jl:

struct Pig <: AbstractAnimal end

sound(pig::Pig) = "oink"

pig = Pig()

sound(pig) # "oink"

why(pig) # The `sound(pig::Pig)` function is invisible to the why(a) function.
  • How can I get why(pig) to work in a Pluto.jl notebook?
  • I’ve provided a notebook that you can try for yourself in Pluto.jl to see the problem yourself.
2

The problem is the definition of the method sound in the notebook. See this section of the manual: Modules · The Julia Language

The code in the linked notebook defines a new function Main.sound rather than implementing a new method for ProblematicAnimals.sound. You have two choices to fix it, the easiest is to fully qualify the name when defining the new method.

ProblematicAnimals.sound(pig::Pig) = "oink"

The other is to import that method as described in the manual in the block at the top of the notebook.

2 Likes
3

Thank you so much. That was a nice Christmas present.