On: Ask YC: What exactly is so hard about OO?

[Zak]

Good abstractions don't require you to understand the whole stack. Effective use of a function, for example requires you to know:

* What the valid arguments are

* What will be returned

* What, if any side effects calling the function will cause

* (sometimes) What resources the function will utilize

Use of most other data types is simpler. Your framework or library should give you this information in the documentation. If your development environment is reasonably friendly, it will give you the arguments, and in many cases, you'll be able to guess the rest of it based on the function name.

If you have to RTFS to figure out how to use your libraries, something is wrong. Institutionalizing that by always putting the source right in front of you is a Bad Thing.

[aston → Zak]

I'm not arguing against abstraction. I'm arguing that explicitly wiring between components is better than implicit.

To make this concrete, take the example of implementing getters for a class in Python. If my class has four fields

  class GetterDone:
    a = 1
    b = 2
    c = 3
    d = 4

I can do something like this inside the class to implement getters:

    def get_a(self):
       return self.a
    def get_b(self):
       return self.b
    def get_c(self):
       return self.c
    def get_d(self):
       return self.d

Or I can do something like this:

    def __getattr__(self, attr):
      if attr.startswith("get_"):
        return lambda: getattr(self, attr[4:])
    raise AttributeError

The latter does a good job of eliminating boilerplate, but at the cost of making it near impossible for me to find out how get_a() is implemented (assuming this was buried in a huge codebase).

[DougBTX → aston]

Assuming you know the core Ruby library, would you call this explicit or implicit?

    class GetterDone
      attr_reader :a, :b, :c, :d
    end

Rather than being a runtime attr.startswith check, this will generate actual "return self.foo" methods in the class.

Think of this as generating code using a UI, except you record the minimal UI commands, rather than putting the full output into your source files. The commands themselves are still explicit, it's just that they contain only the interesting information with the minimum amount of boilerplate.

[aston → DougBTX]

What you're talking about is essentially a syntax specifically for getters, I think (I don't know Ruby that well). I guess my general point about "too much magic" goes away when the magic is part of the language, just on semantics. That is, you don't know the language if you don't know what magic its syntax does.

[sofal → aston]

I don't believe that a typical Java IDE provides a clean enough abstraction to make code generation a big benefit. When it comes down to it, you're still looking at a window full of all the code that the IDE spit out for you. Think of code generation via a compiler versus code generation via an IDE. The code that you see in the window of your IDE should be solely for human eyes. If a lot of it can be trivially automated, then it doesn't deserve space in that window.

[stcredzero → aston]

I'm not 100% sure, but attr_reader looks like it's actually a message send. If it's not, then it could be implemented that way.

[LogicHoleFlaw → stcredzero]

Yes, it is a plain old method being executed in the context of the current class. It creates new class methods which can be used to read, but not write, instance variables.

There are methods to create read-write and (I think? write-only) properties as well.

[lisper → aston]

Or you can just realize that get_X is the Wrong Thing and you should just write GetterDoneInstance.X instead.

[aston → lisper]

Great job ignoring the substance. I thought it'd be better to come up with an unrealistic but simple example rather than to paste in the source for Pylons...

Just play along and imagine a more complex world. If it makes you happier, pretend the getter is intended to return the string version of the numbers or some other operation that would make just using instance.a wrong.

[lisper → aston]

But using instance.a is not wrong because you can override __getattr__. And if overriding __getattr__ is not the right thing then what you are writing is not a getter. Under no circumstances is it justified IMHO to write a get_X method. (And if your language doesn't let you override __getattr__ then you need a better language.) IMHO of course.