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> The defining characteristic of OOP is that hidden state. Hidden state is the characteristic of abstraction, period. OOP has no special claim to it.

lmm 8y ago
Nonsense. Most abstraction isn't about state at all (you won't find state anywhere in the definition of a group, say). You can of course abstract over the difference between having state and not having it (as OO does), but that's a virtually useless abstraction because it doesn't preserve any nontrivial rules/symmetries.
- thrmsforbfast 8y ago
  Perhaps a better way of saying is is that hidden data is a characteristic of abstraction. Which is certainly fair, and fits the analogy to algebra quite well. But in any case, parent's comment that "OOP has no special claim" to hidden state/data (or abstraction) is sound; after all, ADTs already do that.
  - lmm 8y ago
    > Perhaps a better way of saying is is that hidden data is a characteristic of abstraction. Which is certainly fair, and fits the analogy to algebra quite well. I'd disagree with even that much; I'd say abstraction is much more about parameterisation - factoring out the common structure from different constructions - than outright hiding anything. > But in any case, parent's comment that "OOP has no special claim" to hidden state/data (or abstraction) is sound; after all, ADTs already do that. ADTs don't hide mutable state. That much is something OO has a special claim to.
    - thrmsforbfast 8y ago
      "hiding data" and "factoring out the common structure" are almost always intrinsically connected in software systems, because if you can poke at the data then you can violate contracts that give rise to the common structure. This is particularly true of software, but I'd argue it's also true of basically every branch of mathematics outside of a few particular sub-fields of algebra (which are either extremely simple or extremely abstract, and often both). > ADTs don't hide mutable state. That much is something OO has a special claim to. How so? Abstract datatypes certainly hide mutable state. Just because a language doesn't have the "private" keyword doesn't mean that internal data can't be excluded from the interface... this was done all the time in e.g. C without the message passing semantics that characterize OO languages.
      - lmm 8y ago
        > if you can poke at the data then you can violate contracts that give rise to the common structure. Maybe if you can mutate it, but having it be visible isn't an issue. > Abstract datatypes certainly hide mutable state. ADTs are normally understood to be values i.e. immutable. Hidden structure is not the same thing as hidden state.
- danharaj 8y ago
  > Most abstraction isn't about state at all (you won't find state anywhere in the definition of a group, say). Sure, but you also wouldn't care that π is defined as an equivalence class of cauchy sequences if you're treating (R, +) as a group. In fact, one does not care at all about the particular details of a group being a set-- one treats groups up to isomorphism. But of course, I was talking about abstraction in programming.
  - lmm 8y ago
    > Sure, but you also wouldn't care that π is defined as an equivalence class of cauchy sequences if you're treating (R, +) as a group. In fact, one does not care at all about the particular details of a group being a set-- one treats groups up to isomorphism. You don't care at that point, but you don't destroy the information either. You know that (R, +) forms a group and you might use that group structure to, say, efficiently sum a list of reals - but you know that the answer is a real and not just a "group element", and you would go back to doing real-specific operations on your total. So it's more about parameterisation than about outright hiding information. > But of course, I was talking about abstraction in programming. What's the difference? If you don't mean the normal kind of abstraction then what's the definition of the thing that you're talking about?
    - danharaj 8y ago
      > You don't care at that point, but you don't destroy the information either. You know that (R, +) forms a group and you might use that group structure to, say, efficiently sum a list of reals - but you know that the answer is a real and not just a "group element", and you would go back to doing real-specific operations on your total. So it's more about parameterisation than about outright hiding information. When you reason about something as a group, that reasoning operates with the details hidden. When you apply that abstract reasoning to a concrete problem, of course that information is still there. Abstraction is a boundary that looks different on either side. In a similar vein of your example, the compiler knows all the information you're hiding through your program abstractions, but from the point of view of pieces of your code, that abstraction has hidden something. > What's the difference? If you don't mean the normal kind of abstraction then what's the definition of the thing that you're talking about? The word abstraction is so... abstract that it isn't actually a uniform concept applied in different areas but instead many similar concepts that look the same if you squint. The concept I'm talking about is abstraction in the context of program structure. This is more related to mathematical abstraction than a mere metaphor but it's not exactly the same thing as the abstraction in a definition like groups, nor is it the same abstract as in abstract art.
avmich 8y ago
So if all fields are public the object is still the object, not a data structure?

lmm 8y ago

Nonsense. Most abstraction isn't about state at all (you won't find state anywhere in the definition of a group, say). You can of course abstract over the difference between having state and not having it (as OO does), but that's a virtually useless abstraction because it doesn't preserve any nontrivial rules/symmetries.

thrmsforbfast 8y ago
Perhaps a better way of saying is is that hidden data is a characteristic of abstraction. Which is certainly fair, and fits the analogy to algebra quite well. But in any case, parent's comment that "OOP has no special claim" to hidden state/data (or abstraction) is sound; after all, ADTs already do that.
- lmm 8y ago
  > Perhaps a better way of saying is is that hidden data is a characteristic of abstraction. Which is certainly fair, and fits the analogy to algebra quite well. I'd disagree with even that much; I'd say abstraction is much more about parameterisation - factoring out the common structure from different constructions - than outright hiding anything. > But in any case, parent's comment that "OOP has no special claim" to hidden state/data (or abstraction) is sound; after all, ADTs already do that. ADTs don't hide mutable state. That much is something OO has a special claim to.
  - thrmsforbfast 8y ago
    "hiding data" and "factoring out the common structure" are almost always intrinsically connected in software systems, because if you can poke at the data then you can violate contracts that give rise to the common structure. This is particularly true of software, but I'd argue it's also true of basically every branch of mathematics outside of a few particular sub-fields of algebra (which are either extremely simple or extremely abstract, and often both). > ADTs don't hide mutable state. That much is something OO has a special claim to. How so? Abstract datatypes certainly hide mutable state. Just because a language doesn't have the "private" keyword doesn't mean that internal data can't be excluded from the interface... this was done all the time in e.g. C without the message passing semantics that characterize OO languages.
    - lmm 8y ago
      > if you can poke at the data then you can violate contracts that give rise to the common structure. Maybe if you can mutate it, but having it be visible isn't an issue. > Abstract datatypes certainly hide mutable state. ADTs are normally understood to be values i.e. immutable. Hidden structure is not the same thing as hidden state.
danharaj 8y ago
> Most abstraction isn't about state at all (you won't find state anywhere in the definition of a group, say). Sure, but you also wouldn't care that π is defined as an equivalence class of cauchy sequences if you're treating (R, +) as a group. In fact, one does not care at all about the particular details of a group being a set-- one treats groups up to isomorphism. But of course, I was talking about abstraction in programming.
- lmm 8y ago
  > Sure, but you also wouldn't care that π is defined as an equivalence class of cauchy sequences if you're treating (R, +) as a group. In fact, one does not care at all about the particular details of a group being a set-- one treats groups up to isomorphism. You don't care at that point, but you don't destroy the information either. You know that (R, +) forms a group and you might use that group structure to, say, efficiently sum a list of reals - but you know that the answer is a real and not just a "group element", and you would go back to doing real-specific operations on your total. So it's more about parameterisation than about outright hiding information. > But of course, I was talking about abstraction in programming. What's the difference? If you don't mean the normal kind of abstraction then what's the definition of the thing that you're talking about?
  - danharaj 8y ago
    > You don't care at that point, but you don't destroy the information either. You know that (R, +) forms a group and you might use that group structure to, say, efficiently sum a list of reals - but you know that the answer is a real and not just a "group element", and you would go back to doing real-specific operations on your total. So it's more about parameterisation than about outright hiding information. When you reason about something as a group, that reasoning operates with the details hidden. When you apply that abstract reasoning to a concrete problem, of course that information is still there. Abstraction is a boundary that looks different on either side. In a similar vein of your example, the compiler knows all the information you're hiding through your program abstractions, but from the point of view of pieces of your code, that abstraction has hidden something. > What's the difference? If you don't mean the normal kind of abstraction then what's the definition of the thing that you're talking about? The word abstraction is so... abstract that it isn't actually a uniform concept applied in different areas but instead many similar concepts that look the same if you squint. The concept I'm talking about is abstraction in the context of program structure. This is more related to mathematical abstraction than a mere metaphor but it's not exactly the same thing as the abstraction in a definition like groups, nor is it the same abstract as in abstract art.

avmich 8y ago

So if all fields are public the object is still the object, not a data structure?