Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Classes vs. Data Structures

blog.cleancoder.com

Post reply on HN
Print view View original

51–60 of 184 posts

Re: Classes vs. Data Structures

#51

Post by micimize »

Seems to me that with the definitions given, structures and objects aren't opposites, they're corollaries.

A database table is both a data structure and a collection of functions for accessing/manipulating it (SQL). An ORM maps between the "Object Oriented" objects and the "Relational" objects that are tables.

Interesting the author thinks about the the api exposed by a table as the "data structure" itself rather than an object. Pragmatically, we tend to refer to the "objects" at the lower level of abstraction as data structures. Is [...] a function that defines an array, or the array itself?

Re: Classes vs. Data Structures

#52

Post by OJFord »

stupidcar wrote: post #35

Whenever I hear "Socratic dialog", I reach for my revolver. Is there any other form of teaching so irritating and patronising? You might have a brilliant store of insight to impart, but if you insist on trying to do so via a twee, affected and unbelievable conversation with a Mary Sue wise professor, I'm going to write you off as insufferable before the fawning moron you have as proxy for your audience utters their f…

Could it really be that bad?

    I followed the link, it's so much worse.
Worse?

    Yes.
How much worse?

    So much.

Re: Classes vs. Data Structures

#53

Post by lmm »

antisemiotic wrote: post #13
hudon wrote: post #3

The claim that "an object is a set of functions that operate on implied data elements" has a strange corollary because of how in modern OO languages like Java or C#, there is no syntax or popular naming convention to tell the difference between a data structure and an Object. For example, in Java, a LinkedList object is actually not a linked list, it is a set of functions that operate on an implied linked list. If th…

In Haskell this can be pushed further, by making existential types, i.e. opaque type that's only known to implement some type class. This doesn't seem to be that useful in Haskell (I think it's because of the immutability), but trait objects in Rust are pretty much the same and are used more often. As a side note, I hope that the situation with pre- and postcondition checking improves (runtime verficiation like in Ra…

> This doesn't seem to be that useful in Haskell (I think it's because of the immutability)

I suspect it's because of the polymorphism. Why write a function that operates on some unknown a for which a Foo implementation exists when it's so easy to write a function that operates on any a for which a Foo implementation exists?

The only time I've seen existentials used is for safety - in particular ST-style monads where a fancy type is used to ensure that you can't "leak" state out of the monadic context.

Re: Classes vs. Data Structures

#54

Post by evancordell »

chongli wrote: post #49
stupidcar wrote: post #35

Whenever I hear "Socratic dialog", I reach for my revolver. Is there any other form of teaching so irritating and patronising? You might have a brilliant store of insight to impart, but if you insist on trying to do so via a twee, affected and unbelievable conversation with a Mary Sue wise professor, I'm going to write you off as insufferable before the fawning moron you have as proxy for your audience utters their f…

Is there any other form of teaching so irritating and patronising? It's only patronizing to people who are motivated self-learners, such as you. To people who are unmotivated and/or struggling with the concepts (such as high school students), it works better than most other styles I've tried. I've spent a lot of time tutoring high school and elementary school students. Many of them are so frustrated that they just wa…

Is there a difference between using the Socratic method interactively and transcribing a socratic discourse that never occurred?

Re: Classes vs. Data Structures

#55

Post by chongli »

evancordell wrote: post #54
chongli wrote: post #49

Earlier quoted context omitted.

Is there any other form of teaching so irritating and patronising? It's only patronizing to people who are motivated self-learners, such as you. To people who are unmotivated and/or struggling with the concepts (such as high school students), it works better than most other styles I've tried. I've spent a lot of time tutoring high school and elementary school students. Many of them are so frustrated that they just wa…

Is there a difference between using the Socratic method interactively and transcribing a socratic discourse that never occurred?

A huge difference. Interactively, you can both ask and answer questions and you can steer the dialogue toward the pupil's areas of ignorance.

As a form of writing, you're left to guess at what your pupil might be thinking. Apart from Plato, few people have ever managed to succeed at this.

Re: Classes vs. Data Structures

#56

Post by bendbro »

ivan_gammel wrote: post #42
bendbro wrote: post #40

This doesn't make sense to me: "Right. Now consider the area function. Its going to have a switch statement in it, isn’t it?" Perhaps I am nitpicking, or perhaps I am reading this wrong, but I would not design the square data structure to have a perimeter function. The square data structure should just expose the data that describes a square (length, width). Adding higher abstractions (perimeter, etc) on top of the d…

You are getting it wrong. Data structures do not own functions, instead they are passed to functions. So you have shapes and somewhere else you have perimeter function which has switch statement to determine the algorithm of calculation based on the type of the structure.

Ah, and what owns these functions?

And more pressingly, why would you ever pass a data structure to a function that had more than one algorithm to compute a result? The data structure (or perhaps some intermediary (an adapter?)) should own the algorithm within a function that computes only on that data structure. This ensures that all methods associated with your data structure are obviously and explicitly associated (in a single file, class, whatever). The alternative, as outlined in the dialog, is to spread a bunch of switches all around your code. Given these two possibilities, why would one choose to place switches in disparate places throughout your code?

Re: Classes vs. Data Structures

#57

Post by narag »

chongli wrote: post #49
stupidcar wrote: post #35

Whenever I hear "Socratic dialog", I reach for my revolver. Is there any other form of teaching so irritating and patronising? You might have a brilliant store of insight to impart, but if you insist on trying to do so via a twee, affected and unbelievable conversation with a Mary Sue wise professor, I'm going to write you off as insufferable before the fawning moron you have as proxy for your audience utters their f…

Is there any other form of teaching so irritating and patronising? It's only patronizing to people who are motivated self-learners, such as you. To people who are unmotivated and/or struggling with the concepts (such as high school students), it works better than most other styles I've tried. I've spent a lot of time tutoring high school and elementary school students. Many of them are so frustrated that they just wa…

The problem here is that this is a piece of opinion, presented as a lesson, implying that the author is the master and the readers the apprentices.

Re: Classes vs. Data Structures

#58

Post by EGreg »

OJFord wrote: post #52
stupidcar wrote: post #35

Whenever I hear "Socratic dialog", I reach for my revolver. Is there any other form of teaching so irritating and patronising? You might have a brilliant store of insight to impart, but if you insist on trying to do so via a twee, affected and unbelievable conversation with a Mary Sue wise professor, I'm going to write you off as insufferable before the fawning moron you have as proxy for your audience utters their f…

Could it really be that bad? I followed the link, it's so much worse. Worse? Yes. How much worse? So much.

How much?

Re: Classes vs. Data Structures

#59

Post by ci5er »

thom wrote: post #39
stupidcar wrote: post #35

Whenever I hear "Socratic dialog", I reach for my revolver. Is there any other form of teaching so irritating and patronising? You might have a brilliant store of insight to impart, but if you insist on trying to do so via a twee, affected and unbelievable conversation with a Mary Sue wise professor, I'm going to write you off as insufferable before the fawning moron you have as proxy for your audience utters their f…

The only thing more annoying is when people ape Why's (Poignant) Guide to Ruby and you have to follow the adventures of some tedious otter as it meets the rabbit people who ultimately explain pointers in a way which takes a thousand too many words.

Have you ever come across anything that explains why pointers are hard for some people?

I find it difficult to explain pointers to people because I don't understand what they are missing. I could use some help understanding their lack of understanding.

When they don't get "indirect reference to the address of a data structure or object in memory", I'm stuck on how to proceed. Pointing people to the very elegant treatment of this topic in the old K&R doesn't always do the trick. Somehow.

Re: Classes vs. Data Structures

#60

Post by ivan_gammel »

bendbro wrote: post #56
ivan_gammel wrote: post #42

Earlier quoted context omitted.

You are getting it wrong. Data structures do not own functions, instead they are passed to functions. So you have shapes and somewhere else you have perimeter function which has switch statement to determine the algorithm of calculation based on the type of the structure.

Ah, and what owns these functions? And more pressingly, why would you ever pass a data structure to a function that had more than one algorithm to compute a result? The data structure (or perhaps some intermediary (an adapter?)) should own the algorithm within a function that computes only on that data structure. This ensures that all methods associated with your data structure are obviously and explicitly associated…

Did you ever write a program on C? In procedural languages functions are either global or, sometimes, encapsulated in namespaces or modules. Data structures come from that world and do not encapsulate any behavior. In object-oriented languages like Java data structures simply do not exist and are usually emulated via anemic models.
Post reply on HN