Is Julia's way of OOP superior to C++/Python? Why Julia doesn't use class-based OOP?

Internals & Design
84

I try an keep a list of small clear cases where multiple dispatch is a undisputabled better solution

1. Structured Matrix Multiplication.

I have this written up full here, so can read that blog post (or watch the talk version which is at the top of the page)
https://www.oxinabox.net/2020/02/09/whycompositionaljulia.html#are-there-real-world-use-cases-for-multiple-dispatch-

2. Arithmetic Type Promotion

Turns out this is really hard.
A few years ago a large proposal to overhaul Swift’s Integer type was written.
Even in this large document, they explictly:

DOES NOT solve the integer promotion problem, which would allow mixed-type arithmetic. However, we believe that it is an important step in the right direction.

To understand type promotion and why it needs multiple dispatch consider;

  • +(::Int32, ::Float64)::Float64
  • +(::Float64, ::Int32)::Float64
  • +(::Complex{Int32}, ::Float64)::Complex{Float64}

The resulting type depends on both input types, and not in a trivial way either.

3. Contextual Formatting of Objects

IIRC @thautwarm said on twitter something like “The quality of a language can be determined by how hard it is to access polymorpic printing methods”
Which I took to mean this.

This applies to julias whole show(::IO, ::Mime, ::Object), but lets sep away from that to think about generating some document.

Lets consider that was have verious objects that need to be displayed:

  • Number
  • Text
  • Equation

And variouis contexts with in the document to display them:

  • FlowingContent
  • Diagram
  • Table

So consider the options:

  • Number in general should be shown using proportional figures
  • Numbers inside Tables should be shown with tabular figures
  • Anything in FlowingContent should be shown in serifed font
  • Anything in Diagrams should be shown in with a sanserifed font
  • Except Equations in Diagrams should be shown in large sized serifed font
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