Above example is from julia. Julia structs have C layout and have no member functions. The analog of "classes" in julia are "abstract types"; e.g. `AbstractArr

Above example is from julia. Julia structs have C layout and have no member functions. The analog of "classes" in julia are "abstract types"; e.g. `AbstractArray{T}` is anything that implements the AbstractArray interface and holds objects of type T. Abstract types have no instances (all objects have a concrete type, that may be a subtype of an abstract type). Binary compatibility between class and superclass is a cool feature in many OOP languages. This allows fast dynamic dispatch via vtable and lots of shared binary code for non-virtual methods (you can always memory pun from class to superclass). Julia does not support that feature: your different methods can share source code, but they get compiled separately. This is good for performance (more aggressive inlining) and bad for compiling small shared libraries (it is very painful to create julia apps/libs that work without invoking the JIT-compiler at runtime; can be done via custom sysimg). In some sense, julia is not very well suited to closed source business models.