 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Java Forum / General / August 2006J2SE 5.0 Generics and C++ Templates
Hi all, Is there any relation between the J2se 5.0 generics and C++ templates ?? Regards, Sarathy > Is there any relation between the J2se 5.0 generics and > C++ templates ?? Not really, no, except in concept.  SignatureDarryl L. Pierce <mcpierce@gmail.com> Visit my homepage: <http://mcpierce.multiply.com> "By doubting we come to inquiry, through inquiry truth." - Peter Abelard -- Posted via a free Usenet account from http://www.teranews.com >> Is there any relation between the J2se 5.0 generics and >> C++ templates ?? > > Not really, no, except in concept. Not really, no, except in *syntax*. C++ templates are a code-generation mechanism. Java Generics are a type-constraint system which generate no code at all. >>> Is there any relation between the J2se 5.0 generics and C++ >>> templates ?? [quoted text clipped - 4 lines] > > C++ templates are a code-generation mechanism. Which is implementation, and why I said "in concept". > Java Generics are a type-constraint system which generate no code at > all. But both work on the same basic concept: providing a mechanism for writing code in a generic way and allowing a developer to specify the desired functionality at compile-time. SignatureDarryl L. Pierce <mcpierce@gmail.com> Visit my homepage: <http://mcpierce.multiply.com> "By doubting we come to inquiry, through inquiry truth." - Peter Abelard -- Posted via a free Usenet account from http://www.teranews.com >> C++ templates are a code-generation mechanism. > > Which is implementation, and why I said "in concept". I think it's more than just implementation actually. C++ templates are *conceptually* associated with the idea of 'instantiation' per type. > But both work on the same basic concept: providing a mechanism for > writing code in a generic way and allowing a developer to specify the > desired functionality at compile-time. Desired functionality generally *is* specified at compile-time by developers! There's nothing unique to templates/generics about that! Doesn't leave much. I agree that they both provide mechanisms for writing code in a type-generic way. > Doesn't leave much. I agree that they both provide mechanisms for > writing code in a type-generic way. So: type generic code, and angle brackets. That's it? > So: type generic code, and angle brackets. That's it? I think so, and to be honest I wish Java didn't have the angle brackets. > I think so, and to be honest I wish Java didn't have the angle brackets. At least the Java parser understands that << doesn't /always/ mean "right shift"... BTW, I think you are over-stating the similarity between Java's generics and C++'s templates. IMO, they are very different semantically, the overlap is that they have superficially similar syntax, and that they are sometimes used for the same things. But the fact that they are used for some of the same things, doesn't mean they are the same, or even similar. Higher-order functions and objects are also used for (sometimes) similar things, but that doesn't mean they are the same. -- chris > > I think so, and to be honest I wish Java didn't have the angle brackets. > > At least the Java parser understands that << doesn't /always/ mean "right > shift"... That would be the lexer rather than the parser -- and of course, a right shift would be '>>' rather than '<<'. The next version of C++ will also (apparently) change the lexer so '>>' can be treated as two symbols. Personally, I'm not entirely thrilled about that though -- there's code that's currently legitimate that could become ill formed and/or change meaning when this change happens. I'm fairly sure I've never seen real code like this though, so it's probably not a big deal. SignatureLater, Jerry. The universe is a figment of its own imagination. >>I think so, and to be honest I wish Java didn't have the angle brackets. > > BTW, I think you are over-stating the similarity between Java's generics and > C++'s templates. Overstating? everybody else thought I was understating! I got it down to 'type-generic code' (not my term): wasn't that far enough? >>> I think so, and to be honest I wish Java didn't have the angle brackets. >> [quoted text clipped - 3 lines] > > Overstating? Yes. everybody else thought I was understating! I got it down to > 'type-generic code' (not my term): wasn't that far enough? Java Generics do not support specializations nor do they support parametrization of non-types. These two key features lead C++ templates to greatly differ from Java generics. >>>> I think so, and to be honest I wish Java didn't have the angle >>>> brackets. [quoted text clipped - 13 lines] > parametrization of non-types. These two key features lead C++ templates > to greatly differ from Java generics. Thank you. We are in complete agreement and that follows directly from what I said earlier in the thread. I think someone is quoting the wrong poster. [me:] > > BTW, I think you are over-stating the similarity between Java's > > generics and C++'s templates. > > Overstating? everybody else thought I was understating! I got it down to > 'type-generic code' (not my term): wasn't that far enough? Perhaps I misunderstood you. Looking back, you certainly started out in the "right" place: [are generics similar to templates ?] > Not really, no, except in *syntax*. > C++ templates are a code-generation mechanism. Java Generics are a > type-constraint system which generate no code at all. But then seemed to dilute your position to allow that there was some meaningful conceptual similarity -- which I would dispute. My apologies if I misrepresented you. -- chris >> So: type generic code, and angle brackets. That's it? > > I think so, and to be honest I wish Java didn't have the angle brackets. *chuckles...* > > So: type generic code, and angle brackets. That's it? > > I think so, and to be honest I wish Java didn't have the angle brackets. I agree. Those brackets are darn ugly. RS >>> C++ templates are a code-generation mechanism. >> >> Which is implementation, and why I said "in concept". > > I think it's more than just implementation actually. C++ templates are > *conceptually* associated with the idea of 'instantiation' per type. And, as you said, C++ templates generate new code. Java generics do not. That's an implementation detail that completely separates the two otherwise conceptual similar systems. SignatureDarryl L. Pierce <mcpierce@gmail.com> Visit my homepage: <http://mcpierce.multiply.com> "By doubting we come to inquiry, through inquiry truth." - Peter Abelard -- Posted via a free Usenet account from http://www.teranews.com > And, as you said, C++ templates generate new code. Java generics do not. > That's an implementation detail that completely separates the two > otherwise conceptual similar systems. Code generation is carried out for and only for the purpose of template instantiation, and as I said instantiation is a conceptual attribute not just an implementation attribute, so I disagree. >> And, as you said, C++ templates generate new code. Java generics do >> not. That's an implementation detail that completely separates the two >> otherwise conceptual similar systems. > > Code generation is carried out for and only for the purpose of template > instantiation, Does the template specification say that that is what templates are intended to do? Or is it simply the mechanism for fulfilling the specification? SignatureDarryl L. Pierce <mcpierce@gmail.com> Visit my homepage: <http://mcpierce.multiply.com> "By doubting we come to inquiry, through inquiry truth." - Peter Abelard -- Posted via a free Usenet account from http://www.teranews.com >>> And, as you said, C++ templates generate new code. Java generics do >>> not. That's an implementation detail that completely separates the [quoted text clipped - 6 lines] > intended to do? Or is it simply the mechanism for fulfilling the > specification? From the ARM: 'A class template defines the layout and operations for an unbounded set of related types [BTW 'related' is a dubious claim] ... a single function template sort() might define a common definition for sorting all the types defined by the List class template ... A template defines a family of types or operations ... The template mechanism ... allows close to optimal run-time performance through macro expansion of definitions ... A class template specifies how individual classes may be constructed much as a clas declaration specifies how individual objects cabn be constructed ... a class generated from a class template is called a template class ... here, vector<int> and vector<complex> are template classes, and their definitions will by default be generated from the vector template ...' I could go on. It's entirely clear that C++ templates *generate new types*. Every template class is a new class, and the template itself is not a class at all. A Java generic is a type-constrained notation for a single class. > I could go on. It's entirely clear that C++ templates *generate new > types*. Every template class is a new class, and the template itself is > not a class at all. A Java generic is a type-constrained notation for a > single class. And it still an implementation detail of how the concept (about which is what I spoke originally) is fulfilled, the concept being to write code in a very generic way. C++ generates a whole new class while Java doesn't, but that's immaterial to them both sharing the same concept. So my original statement: ---8<[snip]--- sarathy wrote: > Is there any relation between the J2se 5.0 generics and > C++ templates ?? Not really, no, except in concept. ---8<[snip]--- is spot on true. I don't understand why you think that C++ generating a new type while Java doesn't somehow means that conceptually the two aren't at all similar... SignatureDarryl L. Pierce <mcpierce@gmail.com> Visit my homepage: <http://mcpierce.multiply.com> "By doubting we come to inquiry, through inquiry truth." - Peter Abelard -- Posted via a free Usenet account from http://www.teranews.com > I don't understand why you think that C++ generating a > new type while Java doesn't somehow means that conceptually the two > aren't at all similar... Well I don't, and apparently neither does anyone else here. In fact I don't understand how you think that this difference isn't both conceptual and fundamental. The 'similarity' is so superficial as to be merely syntactical, as I said originally, or to amount to no more than a way of doing some kind of type-generic programming, as I said later and was castigated for, probably rightly. >> I don't understand why you think that C++ generating a new type while >> Java doesn't somehow means that conceptually the two aren't at all [quoted text clipped - 3 lines] > don't understand how you think that this difference isn't both > conceptual and fundamental. Whatever. SignatureDarryl L. Pierce <mcpierce@gmail.com> Visit my homepage: <http://mcpierce.multiply.com> "By doubting we come to inquiry, through inquiry truth." - Peter Abelard -- Posted via a free Usenet account from http://www.teranews.com > In fact I > don't understand how you think that this difference isn't both > conceptual and fundamental. The 'similarity' is so superficial as to be > merely syntactical, as I said originally, or to amount to no more than a > way of doing some kind of type-generic programming, as I said later and > was castigated for, probably rightly. I wasn't following the thread too closely, so I didn't noticed your being catigated, nor what you were castigated for. I actually think you aren't going far enough. Saying that Java generics are a way of doing type-generic programming is incorrect. Inheritance and polymorphism as a singly-rooted inheritance hierarchy are a way of doing generic programming. Generics are a way of adding type system awareness to type-generic programming. In STL algorithms, for example, comparison is done with an overloaded '<' operator or with a functor, both using templates. In Java, the same thing is done with ordinary objects that implement interfaces (Comparable or Comparator) and provide code that is called via polymorphic dispatch. Java generics do not change that fact at all. What they do is provide an expressive enough type system that the compiler can remain aware of types while it evaluates generic programming operations. Therefore, a comparison between templates and generics is somewhat poorly founded, not just because they work differently, but also because they solve different problems. C++ templates provide a very broad mechanism for solving a variety of problems. Java's generics are more precisely aimed at a specific problem -- merely expressing the typing relation -- and therefore look considerably different aside from the angle-brackets. SignatureChris Smith - Lead Software Developer / Technical Trainer MindIQ Corporation > Is there any relation between the J2se 5.0 generics and > C++ templates ?? Hi sarathy: My answer will have a slightly different perspective... The C++ templates mechanism is considered generic programming, so based on that alone, I would have to say "yes" to your question, assuming of course, that the relation between generics in C++ and Java is purely based on concept. I totally agree with everyone else that the implementation of generics in both languages is vastly different. C++ templates have been around quite some time, and are part of the Standard Template Library (STL) that includes a comprehensive set of iterators, containers, and algorithms. I applaude Sun Microsystems for adding generics to Java, because I always found the C++ Standard Template Library (STL) to be a powerful tool for application development. Hope this helps... Sincerely, Mike. --- ACGNJ Java Users Group http://www.javasig.org/ --- > The C++ templates mechanism is considered generic programming, so based > on that alone, I would have to say "yes" to your question, assuming of > course, that the relation between generics in C++ and Java is purely > based on concept. While I don't completely disagree that there is any connection, I think this is likely to be misleading. While templates are a mechanism for generic programming in C++, "generics" in Java are (perhaps confusingly) not a mechanism for generic programming. Rather, they are a mechanism for adding type safety to generic programming. In Java, the mechanism for generic programming is to make use of base classes, including the universal base class Object. That's been done, of course, since Java 1.0. The type system support is the only thing that's new. That said, Java's generics are used mainly in places where generic programming is going on, so they do often appear in the same places as C++ templates -- most obviously, in container and iterator classes and supporting algorithms. > I totally agree with everyone else that the implementation of generics > in both languages is vastly different. I hope I've been able to explain why it's not just the implementation that's different. SignatureChris Smith - Lead Software Developer / Technical Trainer MindIQ Corporation Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
|
Reply to this Message
|
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.