4 ms·

It's surprising to me how few developers, even hardcore OO developers, are able to just give this minimal definition. It's the core of the entire paradigm, that

by chton 12y ago

It's surprising to me how few developers, even hardcore OO developers, are able to just give this minimal definition. It's the core of the entire paradigm, that an object is state and behaviour on that state, and yet everybody always gives some convoluted, hardly understandable-to-a-beginner definition. If you're going to be teaching people, "behaviour and state" should be your starting point, not "a value that maps names to stuff". Seeing how the latter maps to an OO language is not trivial, something it should absolutely be.

shriramkmurthi 12y ago
You should read the chapter. Apparently even Alan Kay doesn't quite agree with your view. Also please note that I did not offer this as a _definition_. What I wrote, quite carefully, was: “pretty much the only thing everyone who talks about objects agrees about”. I stand by that, because there are people who don't agree with what you say.
- chton 12y ago
  Alan Kay disagrees that objects exist to 'encapsulate state'. I agree with him. They also encapulsate behaviour. While it's difficult to get a precise overview of Kay's definition (he never gave them explicitly), this page does a good job of collecting the various bits: http://c2.com/cgi/wiki?AlanKaysDefinitionOfObjectOriented http://c2.com/cgi/wiki?AlanKaysDefinitionOfObjectOriented Notable for the "behaviour and state": 3. Objects have their own memory (in terms of objects). 4. Every object is an instance of a class (which must be an object). 5. The class holds the shared behavior for its instances (in the form of objects in a program list) But my point is that I don't agree that an object is "a value that maps names to stuff". I bet even Alan Kay would disagree, seeing as he was a proponent of the Actor model style of working, where objects exchange messages instead of method calls or values. In that case, there are no names to map, there is incoming data that matches a protocol. The object itself determines what behaviour to enact on its own state. Seeing an object as just values and methods is too simplistic, and at the same time too vague to mean anything. And more importantly, as a first sentence to explain what an object is, it's misleading and will raise a lot more questions later.
  - shriramkmurthi 12y ago
    Diving into the middle of a large and complex document and extrapolating from that is always a dangerous venture. The style of the book is to gradually reveal things as it goes along, often even starting with incorrect statements, because we learn best when we see missteps, not only from perfect solutions. Therefore, there's nothing wrong with "starting from" a statement that may not be where we end up. It's meant to be a pedagogic instrument, not a dictionary or other book of definitions. Every chapter is written in this style.
    - chton 12y ago
      I agree, my gripes are not with the entire document, or even with the chapter in question. I also don't have a problem with starting from a statement that may be wrong in an informative way, it's a valid approach to learn a subject. My problem is that it's not presented as a starting point or even implied that the definition might be wrong. It categorically states "The simplest notion of an object—pretty much the only thing everyone who talks about objects agrees about— is". If it had said "One notion of an object -one that many people who talk about objects agree on- is", all would be dandy. When you're stating things as fact in a document dedicated to learning, they should be solid. My other gripe is that I've heard too many vague, biased or incomplete answers to the question "what is an object". These are structures people use every second of every day, but they've never learned a proper definition for it?
      - klibertp 12y ago
        > My other gripe is that I've heard too many vague, biased or incomplete answers to the question Well, "behaviour and state" is also incomplete, because it fails to mention anything about how you refer to parts of state and particular behaviours. "a mapping of names to values and functions" on the other hand mentions both state ("values") and behaviour (functions) and also tells you that they have names. > they've never learned a proper definition for it? Well, there are many different valid definitions for objects, and even more for OO. There are people who don't know any of them for sure, but I strongly suspect that you've dismissed many good definitions as "vague, biased, incomplete" on the grounds of them not being your preferred one. You did it at least once just now, when you failed to realize that "a mapping of names to values and functions" is the same thing as "[named] behaviour and state".

by chton 12y ago

shriramkmurthi 12y ago

You should read the chapter. Apparently even Alan Kay doesn't quite agree with your view. Also please note that I did not offer this as a _definition_. What I wrote, quite carefully, was: “pretty much the only thing everyone who talks about objects agrees about”. I stand by that, because there are people who don't agree with what you say.

chton 12y ago
Alan Kay disagrees that objects exist to 'encapsulate state'. I agree with him. They also encapulsate behaviour. While it's difficult to get a precise overview of Kay's definition (he never gave them explicitly), this page does a good job of collecting the various bits: http://c2.com/cgi/wiki?AlanKaysDefinitionOfObjectOriented http://c2.com/cgi/wiki?AlanKaysDefinitionOfObjectOriented Notable for the "behaviour and state": 3. Objects have their own memory (in terms of objects). 4. Every object is an instance of a class (which must be an object). 5. The class holds the shared behavior for its instances (in the form of objects in a program list) But my point is that I don't agree that an object is "a value that maps names to stuff". I bet even Alan Kay would disagree, seeing as he was a proponent of the Actor model style of working, where objects exchange messages instead of method calls or values. In that case, there are no names to map, there is incoming data that matches a protocol. The object itself determines what behaviour to enact on its own state. Seeing an object as just values and methods is too simplistic, and at the same time too vague to mean anything. And more importantly, as a first sentence to explain what an object is, it's misleading and will raise a lot more questions later.
- shriramkmurthi 12y ago
  Diving into the middle of a large and complex document and extrapolating from that is always a dangerous venture. The style of the book is to gradually reveal things as it goes along, often even starting with incorrect statements, because we learn best when we see missteps, not only from perfect solutions. Therefore, there's nothing wrong with "starting from" a statement that may not be where we end up. It's meant to be a pedagogic instrument, not a dictionary or other book of definitions. Every chapter is written in this style.
  - chton 12y ago
    I agree, my gripes are not with the entire document, or even with the chapter in question. I also don't have a problem with starting from a statement that may be wrong in an informative way, it's a valid approach to learn a subject. My problem is that it's not presented as a starting point or even implied that the definition might be wrong. It categorically states "The simplest notion of an object—pretty much the only thing everyone who talks about objects agrees about— is". If it had said "One notion of an object -one that many people who talk about objects agree on- is", all would be dandy. When you're stating things as fact in a document dedicated to learning, they should be solid. My other gripe is that I've heard too many vague, biased or incomplete answers to the question "what is an object". These are structures people use every second of every day, but they've never learned a proper definition for it?
    - klibertp 12y ago
      > My other gripe is that I've heard too many vague, biased or incomplete answers to the question Well, "behaviour and state" is also incomplete, because it fails to mention anything about how you refer to parts of state and particular behaviours. "a mapping of names to values and functions" on the other hand mentions both state ("values") and behaviour (functions) and also tells you that they have names. > they've never learned a proper definition for it? Well, there are many different valid definitions for objects, and even more for OO. There are people who don't know any of them for sure, but I strongly suspect that you've dismissed many good definitions as "vague, biased, incomplete" on the grounds of them not being your preferred one. You did it at least once just now, when you failed to realize that "a mapping of names to values and functions" is the same thing as "[named] behaviour and state".