How to create a “single dispatch, object-oriented Class” in julia that behaves like a standard Java Class with public / private fields and methods

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While of course this isn’t the idiomatic way to create objects and methods in julia, there’s nothing horribly wrong with it either. In any language with closures you can define your own “object systems” like this, for example see the many object systems that have been developed within Scheme.

In julia v0.5 there is an especially slick way to do this due to the fact that closures represent their captured variables as object fields automatically. For example:

julia> function Person(name, age)
        getName() = name
        getAge() = age
        getOlder() = (age+=1)
        ()->(getName;getAge;getOlder)
       end
Person (generic function with 1 method)

julia> o = Person("bob", 26)
(::#3) (generic function with 1 method)

julia> o.getName()
"bob"

julia> o.getAge()
26

julia> o.getOlder()
27

julia> o.getAge()
27

It’s weird that you have to return a function to do this, but there it is. This benefits from many optimizations like the language figuring out precise field types for you, so in some cases we can even inline these “method calls”. Another cool feature is that the bottom line of the function controls which fields are “public”; anything listed there will become a field of the object. In this case you get only the methods, and not the name and age variables. But if you added name to the list then you’d be able to do o.name as well. And of course the methods are also multi-methods; you can add multiple definitions for getOlder etc. and it will work like you expect.

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