8 ms·

All-OOP? So functions will be objects too? And classes? And contexts? Not meaning to start a flame, just saying the title's a bit inaccurate IMHO...

c4n4rd 15y ago
This is a very good point. If functions become objects, interfaces would become literally useless. Somehow it seems that it would not be the case since this would be a drastic change (even thought getting rid of primitives are as well.)
- CodeMage 15y ago
  Literally useless? Would you like to elaborate on how specifying a contract that has to be implemented is suddenly useless because you have function types?
  - yummyfajitas 15y ago
    I think the experience of Haskell is relevant here. Once Haskell introduced first class functions, everyone stopped using typeclasses. [edit: apparently my sarcasm was too subtle. HOF and typeclasses are both vitally important pieces of Haskell, which are orthogonal to each other. I'm pretty sure both were in Haskell from day 1. Some code for which both are essential: class Monad m where (>>=) :: m a -> (a -> m b) -> m b (>>) :: m a -> m b -> m b return :: a -> m a fail :: String -> m a ]
    - CodeMage 15y ago
      I'm genuinely curious: is this because Haskell is generally hard to learn[] or because of some inherent property of Haskell that makes type classes unnecessary when you have first class functions? [] This statement is based purely on my own experience. I find the Haskell documentation a bit unfriendly with its "academic" style. The content is great, but the form makes it a bit hard to assimilate. Monads were especially painful.
    - xyzzyz 15y ago
      Once Haskell introduced first class functions, everyone stopped using typeclasses. What do you mean? From what I've seen, everyone uses typeclasses in Haskell.
    - calpaterson 15y ago
      I don't think typeclasses were in from day one, they were added quite late in the development of the language (but some years before H98). I don't think they're in Miranda, for example. Here's a paper introducing them. http://dl.acm.org/citation.cfm?id=227700 http://dl.acm.org/citation.cfm?id=227700
      - yummyfajitas 15y ago
        I stand corrected. I guess Haskell before H98 was a very different language than it is today.
      - SamReidHughes 15y ago
        Type classes were in Haskell 1.0. See http://webcache.googleusercontent.com/search?q=cache:rtFsiQCtqxYJ:www.haskell.org/definition/haskell-report-1.0.ps.gz+&cd=2&hl=en&ct=clnk&gl=us http://webcache.googleusercontent.com/search?q=cache:rtFsiQC...
  - hythloday 15y ago
    Not sure I agree with the GP's point, but I believe he's arguing that when fulfilling the contract of a fictional MouseClickListener: interface MouseClickListener { void mouseClicked(MouseEvent e); } one often uses an anonymous class to do so: void init() { mouse.setClickListener(new MouseClickListener() { void mouseClicked(MouseEvent e) { println(e); } }); } the exact effect could be achieved with a reference to a named function (if Java supported them, which presumably it will once "everything is an object"): void init() { void mouseClick(MouseEvent e) { println(e); } mouse.setClickListener(mouseClick); } given that interfaces are simply syntax for function routing, when you have the ability to reference functions by first-class types (i.e. you have the ability to determine function routing yourself), the set of things that you can only sensibly do with interfaces is a lot smaller. This is how C# delegates work, right? Any Java -> C# programmer want to comment on whether they rely less on interfaces now and what they use them for?
    - eropple 15y ago
      I bounce between Java and C#. I'm not sure at all what he's talking about. I use interfaces all the time in C#. I even specify delegate properties (as distinct from events, when I don't want them to be multicast) in interfaces. I think both concepts are probably independent of one another.
    - bermanoid 15y ago
      First class functions pretty much have no bearing on whether or not interfaces are useful. Sure, one use case for inner classes is to implement interfaces in-place in situations where what you really want to do is just pass a function, and in those cases it's probably better to use a function instead, but the equivalence doesn't go the other way. There are plenty of cases where you really need to pass an object to a function and know that the object supports multiple operations, for instance take a look at Map<K,V>: http://docs.oracle.com/javase/6/docs/api/java/util/Map.html http://docs.oracle.com/javase/6/docs/api/java/util/Map.html There are 14 methods there, and when I write code that takes a Map object, I really mean it - I'm not just using the interface as a hack because I want a function pointer, I need an object that supports all of those methods, and I'm probably going to be using several of them.
- cynicalkane 15y ago
  Clojure has both function objects and interfaces (called 'protocols'). In fact, it encourages the use of interfaces while strongly discouraging the traditional object inheritance model. Most people who've tried it AFIAK consider Clojure a well-designed language.
  - jemeshsu 15y ago
    Clojure, Golang, Scala and Rust all implement similar interface.
- Roboprog 15y ago
  While I agree that I hate interfaces with one method, what about interfaces that actually define several methods (e.g. - perhaps a driver for something that needs to do operations like "open", "close", "get", "put")? Interfaces still serve a purpose bundling together related operations with replaceable implementations. They're just a nuisance for single-purpose functions/functors (e.g. - "run").
kirinan 15y ago
I think similar to C# where the primitives are objects is what they want, terribly misleading title I agree. However, I cringe when I think of what this does to performance. The memory overhead of objects in java is pretty high (relative) while primitives are very memory efficient. If they can make the primitives just as efficient, it would be awesome, but I guess its a wait and see. I don't currently mind using the static classes on the object representation of the primitives to do things.
- chrisb 15y ago
  In C# primitives are not objects, but they can be boxed into objects. So if you have a class: public class X { public Int32 i; public Int32 j; public Int32 k; } Then it takes 12 bytes + single object overhead (which in MS .NET I believe is two pointers). But if you assign a primitive (e.g. Int32) to an variable of type 'object' then it will be boxed and then require the object overhead. A neat thing about C#/.NET is that generics are baked deeply into the platform, so using primitive (actually, any value-type struct) types as generic arguments will not require object memory or casting overheads.
  - bad_user 15y ago
    Well, actually, in C# struct instances ARE objects allocated on the stack, instead of the heap. A parallel can be drawn with C++ in which the user of a class decides on declaration/initialization where to store the object (either on the stack, or on the heap). The difference with C++ is that in C# the author of the class decides where instances of it should be stored, so this decision happens when the class is declared, not when it's used. Otherwise there are few differences between structs and classes and all differences stem from the differences in storage. For example struct instances must be passed by value and not reference, because by definition stack-allocated values are short-lived and playing with references to stack-allocated values is dangerous. Structs must also have an implicit constructor because stack-allocated values cannot be NULL (logically, you need a reference to represent NULL). In my experience, all discussions about what is or isn't an object are counter-productive. What really bugs me about Java is that you cannot build your own types that behave just like the built-in types. For instance you cannot override operators like "+" (which works for primitives or Strings), you cannot override [] (which works for arrays), you cannot declare other stack-allocated structures, arrays are reified and yet you cannot declare your own reified data-structures and so on. The presence of primitives doesn't bother me as much as lacking the means to build my own primitives.
CodeMage 15y ago
Classes are already objects. I don't know whether Java 8 will finally introduce function as a data type, but if it does, I'm pretty sure they won't do it the way Ruby blocks work (i.e. block is not an object).
- rukkyg 15y ago
  Aren't methods already an object of class java.lang.reflect.Method? Do you mean you should be able to do something like foo(PrintStream.println.method) like you can do foo(PrintStream.class)?
  - eternalban 15y ago
    No, a class's methods are not instances of java.lang.reflect.Method. The latter is simply a 'reflection', per the package name, of first class JVM construct e.g. a reflection on a method.
    - riffraff 15y ago
      would you care to explain why this is not enough? You can pass them around, invoke them, get their properties. The interface may be bad but I'm not sure what is missing.
      - eternalban 15y ago
        In the original comment, I was merely addressing the misunderstanding of the GP regarding the reflection packages constructs. The interface is your basic (irreducible) disconnected/unbound procedure invocation API, with all the positive/warts associated. I agree that in principle, we have enough information in the reflection data structure to allow a (specific) JVM implementation to provide a non-standard 'method object' feature. Consensus, possibly? (Good question, really. C. Nutter is one to hit with that one.)
- EdiX 15y ago
  I'd rather they didn't. It would be redundant with inner classes that are already there, I don't like this piling up of features. It would be more interesting if they allowed inner classes to close over non-final variables.

c4n4rd 15y ago

This is a very good point. If functions become objects, interfaces would become literally useless. Somehow it seems that it would not be the case since this would be a drastic change (even thought getting rid of primitives are as well.)

CodeMage 15y ago
Literally useless? Would you like to elaborate on how specifying a contract that has to be implemented is suddenly useless because you have function types?
- yummyfajitas 15y ago
  I think the experience of Haskell is relevant here. Once Haskell introduced first class functions, everyone stopped using typeclasses. [edit: apparently my sarcasm was too subtle. HOF and typeclasses are both vitally important pieces of Haskell, which are orthogonal to each other. I'm pretty sure both were in Haskell from day 1. Some code for which both are essential: class Monad m where (>>=) :: m a -> (a -> m b) -> m b (>>) :: m a -> m b -> m b return :: a -> m a fail :: String -> m a ]
  - CodeMage 15y ago
    I'm genuinely curious: is this because Haskell is generally hard to learn[] or because of some inherent property of Haskell that makes type classes unnecessary when you have first class functions? [] This statement is based purely on my own experience. I find the Haskell documentation a bit unfriendly with its "academic" style. The content is great, but the form makes it a bit hard to assimilate. Monads were especially painful.
  - xyzzyz 15y ago
    Once Haskell introduced first class functions, everyone stopped using typeclasses. What do you mean? From what I've seen, everyone uses typeclasses in Haskell.
  - calpaterson 15y ago
    I don't think typeclasses were in from day one, they were added quite late in the development of the language (but some years before H98). I don't think they're in Miranda, for example. Here's a paper introducing them. http://dl.acm.org/citation.cfm?id=227700 http://dl.acm.org/citation.cfm?id=227700
    - yummyfajitas 15y ago
      I stand corrected. I guess Haskell before H98 was a very different language than it is today.
    - SamReidHughes 15y ago
      Type classes were in Haskell 1.0. See http://webcache.googleusercontent.com/search?q=cache:rtFsiQCtqxYJ:www.haskell.org/definition/haskell-report-1.0.ps.gz+&cd=2&hl=en&ct=clnk&gl=us http://webcache.googleusercontent.com/search?q=cache:rtFsiQC...
- hythloday 15y ago
  Not sure I agree with the GP's point, but I believe he's arguing that when fulfilling the contract of a fictional MouseClickListener: interface MouseClickListener { void mouseClicked(MouseEvent e); } one often uses an anonymous class to do so: void init() { mouse.setClickListener(new MouseClickListener() { void mouseClicked(MouseEvent e) { println(e); } }); } the exact effect could be achieved with a reference to a named function (if Java supported them, which presumably it will once "everything is an object"): void init() { void mouseClick(MouseEvent e) { println(e); } mouse.setClickListener(mouseClick); } given that interfaces are simply syntax for function routing, when you have the ability to reference functions by first-class types (i.e. you have the ability to determine function routing yourself), the set of things that you can only sensibly do with interfaces is a lot smaller. This is how C# delegates work, right? Any Java -> C# programmer want to comment on whether they rely less on interfaces now and what they use them for?
  - eropple 15y ago
    I bounce between Java and C#. I'm not sure at all what he's talking about. I use interfaces all the time in C#. I even specify delegate properties (as distinct from events, when I don't want them to be multicast) in interfaces. I think both concepts are probably independent of one another.
  - bermanoid 15y ago
    First class functions pretty much have no bearing on whether or not interfaces are useful. Sure, one use case for inner classes is to implement interfaces in-place in situations where what you really want to do is just pass a function, and in those cases it's probably better to use a function instead, but the equivalence doesn't go the other way. There are plenty of cases where you really need to pass an object to a function and know that the object supports multiple operations, for instance take a look at Map<K,V>: http://docs.oracle.com/javase/6/docs/api/java/util/Map.html http://docs.oracle.com/javase/6/docs/api/java/util/Map.html There are 14 methods there, and when I write code that takes a Map object, I really mean it - I'm not just using the interface as a hack because I want a function pointer, I need an object that supports all of those methods, and I'm probably going to be using several of them.
cynicalkane 15y ago
Clojure has both function objects and interfaces (called 'protocols'). In fact, it encourages the use of interfaces while strongly discouraging the traditional object inheritance model. Most people who've tried it AFIAK consider Clojure a well-designed language.
- jemeshsu 15y ago
  Clojure, Golang, Scala and Rust all implement similar interface.
Roboprog 15y ago
While I agree that I hate interfaces with one method, what about interfaces that actually define several methods (e.g. - perhaps a driver for something that needs to do operations like "open", "close", "get", "put")? Interfaces still serve a purpose bundling together related operations with replaceable implementations. They're just a nuisance for single-purpose functions/functors (e.g. - "run").

kirinan 15y ago

I think similar to C# where the primitives are objects is what they want, terribly misleading title I agree. However, I cringe when I think of what this does to performance. The memory overhead of objects in java is pretty high (relative) while primitives are very memory efficient. If they can make the primitives just as efficient, it would be awesome, but I guess its a wait and see. I don't currently mind using the static classes on the object representation of the primitives to do things.

chrisb 15y ago
In C# primitives are not objects, but they can be boxed into objects. So if you have a class: public class X { public Int32 i; public Int32 j; public Int32 k; } Then it takes 12 bytes + single object overhead (which in MS .NET I believe is two pointers). But if you assign a primitive (e.g. Int32) to an variable of type 'object' then it will be boxed and then require the object overhead. A neat thing about C#/.NET is that generics are baked deeply into the platform, so using primitive (actually, any value-type struct) types as generic arguments will not require object memory or casting overheads.
- bad_user 15y ago
  Well, actually, in C# struct instances ARE objects allocated on the stack, instead of the heap. A parallel can be drawn with C++ in which the user of a class decides on declaration/initialization where to store the object (either on the stack, or on the heap). The difference with C++ is that in C# the author of the class decides where instances of it should be stored, so this decision happens when the class is declared, not when it's used. Otherwise there are few differences between structs and classes and all differences stem from the differences in storage. For example struct instances must be passed by value and not reference, because by definition stack-allocated values are short-lived and playing with references to stack-allocated values is dangerous. Structs must also have an implicit constructor because stack-allocated values cannot be NULL (logically, you need a reference to represent NULL). In my experience, all discussions about what is or isn't an object are counter-productive. What really bugs me about Java is that you cannot build your own types that behave just like the built-in types. For instance you cannot override operators like "+" (which works for primitives or Strings), you cannot override [] (which works for arrays), you cannot declare other stack-allocated structures, arrays are reified and yet you cannot declare your own reified data-structures and so on. The presence of primitives doesn't bother me as much as lacking the means to build my own primitives.

CodeMage 15y ago

Classes are already objects. I don't know whether Java 8 will finally introduce function as a data type, but if it does, I'm pretty sure they won't do it the way Ruby blocks work (i.e. block is not an object).

rukkyg 15y ago
Aren't methods already an object of class java.lang.reflect.Method? Do you mean you should be able to do something like foo(PrintStream.println.method) like you can do foo(PrintStream.class)?
- eternalban 15y ago
  No, a class's methods are not instances of java.lang.reflect.Method. The latter is simply a 'reflection', per the package name, of first class JVM construct e.g. a reflection on a method.
  - riffraff 15y ago
    would you care to explain why this is not enough? You can pass them around, invoke them, get their properties. The interface may be bad but I'm not sure what is missing.
    - eternalban 15y ago
      In the original comment, I was merely addressing the misunderstanding of the GP regarding the reflection packages constructs. The interface is your basic (irreducible) disconnected/unbound procedure invocation API, with all the positive/warts associated. I agree that in principle, we have enough information in the reflection data structure to allow a (specific) JVM implementation to provide a non-standard 'method object' feature. Consensus, possibly? (Good question, really. C. Nutter is one to hit with that one.)
EdiX 15y ago
I'd rather they didn't. It would be redundant with inner classes that are already there, I don't like this piling up of features. It would be more interesting if they allowed inner classes to close over non-final variables.