[pjmlp]

As Wirth puts it, Algorithms + Data Structures = Programs

What OOP nicely brings to the table is polymorphism and type extension. Two things not doable just with modules.

Although generics help with static polymorphism.

The problem was that the IT world went overboard with Java and C#, influenced by Smalltalk, Eiffel and other pure OO languages.

Along the way, the world forgot about the other programming languages that offered both modules and objects.

> Blasphemous as it may seem, a switch statement does the equivalent of simple polymorphism and can be kept inline.

Except it is not extendable.

[ufo]

Switch statements are extensible in that you can add extra switch statements to your program without needing to go back and add a method to every class you coded, spread over a dozen different files. Its the old ExpressionProblem tradeoff.

[ANTSANTS]

All code is extensible if you have the source code and can recompile the whole thing then restart the program. I think pjmlp meant extensible in the "extensible at runtime" sense.

[ufo]

switch statements and method calls are kind of duals of each other. One makes it easy to add new classes but fixes the set of methods and the other makes it easy to add new methods but fixes the set of classes. It doesn't have to do with runtime.

http://c2.com/cgi/wiki?ExpressionProblem

[ANTSANTS]

Yeah, I said as much (even calling them duals) in a sibling comment.

https://news.ycombinator.com/item?id=8375910

Method calls don't need to be fixed either. Just because C++ stores virtual methods in a fixed-sized table doesn't mean Lua/Javascript/etc can't store them in hash tables. And a list of hooks is sort of like an extensible switch statement, but bare switch statements like you were describing obviously don't have that kind of runtime flexibility.

[sitkack]

If you get tired of the switch statement, pattern matching is the functional dual of polymorphic dispatch.

[eru]

Even though, pattern matching (and algebraic datatypes) would work just as well in an imperative language as in a function setting.

(Not sure, whether you'd need garbage collection to make pattern matching really useful, though.

[sitkack]

Pattern matching is welcomed everywhere, it saves conditionals and keeps the code clean.

[pjmlp]

If you have control the code.

[wtetzner]

No, you can add new functions that switch over the different types without having control over the code. That way you don't have to add the same method to each of the classes.

It's a different dimension of extensibility.

[kgabis]

> Except it is not extendable.

Function pointers are a good way to achieve extensibility in such cases.

[pjmlp]

You are basically doing a VMT implementation by hand.

I rather let the compiler do the work for me.

[kgabis]

No, using function pointers does not necessarily mean implementing a vtable.

[pjmlp]

No, but it feels like it.

Oberon and Modula-3 only provide record extensions for OOP, with methods being done via function pointers.

In case you aren't familiar with these languages, here is some info.

http://www.inf.ethz.ch/personal/wirth/ProgInOberon.pdf (Chapter 23)

http://en.wikipedia.org/wiki/Modula-3#Object_Oriented

In Oberon's case, which was lucky to have survived longer at ETHZ than Modula-3 did at DEC/Olivetti, all successors (Oberon-2, Active Oberon, Component Pascal, Zonnon) ended up adding support for method declarations.