I have a few related questions about pragmas. What got me started on this line of questions was trying to determine whether it's possible to disable some warnings without going all the way to no worries (I'd still like to worry, at least a little bit!). And I'm still interested in the answer to that specific question.
But thinking about that issue made me realize that I don't really understand how pragmas work. It's clear that at least some pragmas take arguments (e.g., use isms<Perl5>). But they don't seem to be functions. Where do they fit into the overall MOP? Are they sort of like Traits? Or packages? Is there any way to introspect over them? See what pragmas are currently in effect?
Are pragmas built into the language, or are they something that users can add? When writing a library, I'd love to have some errors/warnings that users can optionally disable with a pragma – is that possible, or are they restricted to use in the compiler? If I can create my pragmas, is there a practical difference between setting something with a pragma versus with a dynamic variable, aside from the cleaner look of a pragma? For that matter, how do we decide what language features should be set with a pragma versus a variable (e.g., why is $*TOLERANCE not a pragma)?
Basically, I'd be interested in any info about pragmas that you could offer or point me towards – though my specific question is still whether I can selectively turn off certain warnings.
Currently, pragmas are hard-coded in the handling of the use statement. They usually either set some flag in a hash that is associated with the lexical scope of the moment, or change the setting of a dynamic variable in the grammar.
Since use is a compile time construct, you can only use compile time constructs to get at them (currently) (so you'd need BEGIN if it is not part of a use).
I have been in favour of decoupling use from pragma's in the past, as I see them as mostly a holdover from the Perl roots of Raku.
All of this will be changed in the RakuAST branch. I'm not sure what Jonathan Worthington has in mind regarding pragmas in the RakuAST context. For one thing, I think we should be able to "export" a pragma to the scope of a use statement.
I am using eclipse to develop a web application. Just today I have updated my struts version by changing the JAR file. I am getting warnings at some places that methods are deprecated, but the code is working fine.
I want to know some things
Is it wrong to use Deprecated methods or classes in Java?
What if I don't change any method and run my application with warnings that I have, will it create any performance issue.
1. Is it wrong to use Deprecated methods or classes in Java?
From the definition of deprecated:
A program element annotated #Deprecated is one that programmers are discouraged from using, typically because it is dangerous, or because a better alternative exists.
The method is kept in the API for backward compatibility for an unspecified period of time, and may in future releases be removed. That is, no, it's not wrong, but there is a better way of doing it, which is more robust against API changes.
2. What if I don't change any method and run my application with warnings that I have, will it create any performance issue.
Most likely no. It will continue to work as before the deprecation. The contract of the API method will not change. If some internal data structure changes in favor of a new, better method, there could be a performance impact, but it's quite unlikely.
The funniest deprecation in the Java API, is imo, the FontMetrics.getMaxDecent. Reason for deprecation: Spelling error.
Deprecated. As of JDK version 1.1.1, replaced by getMaxDescent().
You can still use deprecated code without performance being changed, but the whole point of deprecating a method/class is to let users know there's now a better way of using it, and that in a future release the deprecated code is likely to be removed.
Terminology
From the official Sun glossary:
deprecation: Refers to a class, interface, constructor, method or field that is no longer recommended, and may cease to exist in a future version.
From the how-and-when to deprecate guide:
You may have heard the term, "self-deprecating humor," or humor that minimizes the speaker's importance. A deprecated class or method is like that. It is no longer important. It is so unimportant, in fact, that you should no longer use it, since it has been superseded and may cease to exist in the future.
The #Deprecated annotation went a step further and warn of danger:
A program element annotated #Deprecated is one that programmers are discouraged from using, typically because it is dangerous, or because a better alternative exists.
References
java.sun.com Glossary
Language guide/How and When to Deprecate APIs
Annotation Type Deprecated API
Right or wrong?
The question of whether it's right or wrong to use deprecated methods will have to be examined on individual basis. Here are ALL the quotes where the word "deprecated" appears in Effective Java 2nd Edition:
Item 7: Avoid finalizers: The only methods that claim to guarantee finalization are System.runFinalizersOnExit and its evil twin Runtime.runFinalizersOnExit. These methods are fatally flawed and have been deprecated.
Item 66: Synchronize access to shared mutable data: The libraries provide the Thread.stop method, but this method was deprecated long ago because it's inherently unsafe -- its use can result in data corruption.
Item 70: Document thread safety: The System.runFinalizersOnExit method is thread-hostile and has been deprecated.
Item 73: Avoid thread groups: They allow you to apply certain Thread primitives to a bunch of threads at once. Several of these primitives have been deprecated, and the remainder are infrequently used. [...] thread groups are obsolete.
So at least with all of the above methods, it's clearly wrong to use them, at least according to Josh Bloch.
With other methods, you'd have to consider the issues individually, and understand WHY they were deprecated, but generally speaking, when the decision to deprecate is justified, it will tend to lean toward wrong than right to continue using them.
Related questions
Difference between a Deprecated and Legacy API?
Aside from all the excellent responses above I found there is another reason to remove deprecated API calls.
Be researching why a call is deprecated I often find myself learning interesting things about the Java/the API/the Framework. There is often a good reason why a method is being deprecated and understanding these reasons leads to deeper insights.
So from a learning/growing perspective, it is also a worthwhile effort
It certainly doesn't create a performance issue -- deprecated means in the future it's likely that function won't be part of the library anymore, so you should avoid using it in new code and change your old code to stop using it, so you don't run into problems one day when you upgrade struts and find that function is no longer present
It's not wrong, it's just not recommended. It generally means that at this point there is a better way of doing things and you'd do good if you use the new improved way. Some deprecated stuff are really dangerous and should be avoided altogether. The new way can yield better performance than the deprecated one, but it's not always the case.
You may have heard the term, "self-deprecating humor". That is humor that minimizes your importance. A deprecated class or method is like that. It is no longer important. It is so unimportant, in fact, that it should no longer be used at all, as it will probably cease to exist in the future.
Try to avoid it
Generally no, it's not absolutely wrong to use deprecated methods as long as you have a good contingency plan to avoid any problems if/when those methods disappear from the library you're using. With Java API itself this never happens but with just about anything else it means that it's going to be removed. If you specifically plan not to upgrade (although you most likely should in the long run) your software's supporting libraries then there's no problem in using deprecated methods.
No.
Yes, it is wrong.
Deprecated methods or classes will be removed in future versions of Java and should not be used. In each case, there should be an alternative available. Use that.
There are a couple of cases when you have to use a deprecated class or method in order to meet a project goal. In this case, you really have no choice but to use it. Future versions of Java may break that code, but if it's a requirement you have to live with that. It probably isn't the first time you had to do something wrong in order to meet a project requirement, and it certainly won't be the last.
When you upgrade to a new version of Java or some other library, sometimes a method or a class you were using becomes deprecated. Deprecated methods are not supported, but shouldn't produce unexpected results. That doesn't mean that they won't, though, so switch your code ASAP.
The deprecation process is there to make sure that authors have enough time to change their code over from an old API to a new API. Make use of this time. Change your code over ASAP.
It is not wrong, but some of the deprecated methods are removed in the future versions of the software, so you will possibly end up with not working code.
Is it wrong to use Deprecated methods or classes in Java?"
Not wrong as such but it can save you some trouble. Here is an example where it's strongly discouraged to use a deprecated method:
http://java.sun.com/j2se/1.4.2/docs/guide/misc/threadPrimitiveDeprecation.html
Why is Thread.stop deprecated?
Because it is inherently unsafe.
Stopping a thread causes it to unlock
all the monitors that it has locked.
(The monitors are unlocked as the
ThreadDeath exception propagates up
the stack.) If any of the objects
previously protected by these monitors
were in an inconsistent state, other
threads may now view these objects in
an inconsistent state. Such objects
are said to be damaged. When threads
operate on damaged objects, arbitrary
behavior can result. This behavior may
be subtle and difficult to detect, or
it may be pronounced. Unlike other
unchecked exceptions, ThreadDeath
kills threads silently; thus, the user
has no warning that his program may be
corrupted. The corruption can manifest
itself at any time after the actual
damage occurs, even hours or days in
the future.
What if don't change any method and run my application with warnings that I have, will it create any performance issue.
There should be no issues in terms of performance. The standard API is designed to respect some backward compatibility so applications can be gradually adapted to newer versions of Java.
Is it wrong to use Deprecated methods or classes in Java?
It is not "wrong", still working but avoid it as much as possible.
Suppose there is a security vulnerability associated with a method and the developers determine that it is a design flaw. So they may decide to deprecate the method and introduce the new way.
So if you still use the old method, you have a threat. So be aware of the reason to the deprecation and check whether how it affects to you.
what if don't change any method and run my application with warnings that I have, will it create any performance issue.
If the deprecation is due to a performance issue, then you will suffer from a performance issue, otherwise there is no reason to have such a problem. Again would like to point out, be aware of the reason to deprecation.
In Java it's #Deprecated, in C# it's [Obsolete].
I think I prefer C#'s terminology. It just means it's obsolete. You can still use it if you want to, but there's probably a better way.
It's like using Windows 3.1 instead of Windows 7 if you believe that Windows 3.1 is obsolete. You can still use it, but there's probably better features in a future version, plus the future versions will probably be supported - the obsolete one won't be.
Same for Java's #Deprecated - you can still use the method, but at your own risk - in future, it might have better alternatives, and might not even be supported.
If you are using code that is deprecated, it's usually fine, as long as you don't have to upgrade to a newer API - the deprecated code might not exist there. I suggest if you see something that is using deprecated code, to update to use the newer alternatives (this is usually pointed out on the annotation or in a Javadoc deprecated comment).
Edit: And as pointed out by Michael, if the reason for deprecation is due to a flaw in the functionality (or because the functionality should not even exist), then obviously, one shouldn't use the deprecated code.
Of course not - since the whole Java is getting #Deprecated :-) you can feel free to use them for as long as Java lasts. Not going to notice any diff anyway, unless it's something really broken. Meaning - have to read about it and then decide.
In .Net however, when something is declared [Obsolete], go and read about it immediately even if you never used it before - you have about 50% chance that it's more efficient and/or easier to use than replacement :-))
So in general, it can be quite beneficial to be techno-conservative these days, but you have to do your reading chore first.
I feel that deprecated method means; there is an alternate=ive method available which is better in all aspects than existing method. Better to use the good method than existing old method. For backward compatibility, old methods are left as deprecated.
From reading revision N3242 of the c++11 draft, it appears that some components of the standard library's interfaces (notably threading and locking) depend on exception handling.
Since I do a lot of work with exceptions disabled, I am wondering which library components/features will be (practically or logically) unusable without exception handling enabled?
First of all (just as a reminder), disabling exceptions and RTTI are compiler specific extensions the Standard has no consideration for.
Since the Standard Library is usually tied to the compiler, it may be that your implementation of the Standard Library has been specifically designed to cope with this (and in particular, to cope with new returning null pointers instead of raising std::bad_alloc).
Therefore, what you ask for is non-sensical. Check the documentation of your own library for a complete list.
That being said, the Standard does guarantee that a number of operations will never throw. I don't know of any operation that swallows exceptions, I would suppose that most of them are actually safe to use as-is.
For example, all algorithms should be safe.
Still, once again, I can only recommend reading the documentation of your implementation.
This question is over one month old, and unanswered.
I am providing an answer which can be considered a community wiki, add to it as needed.
std::thread Section 30.2.2. Transitive. Abstraction implemented using native implementations.
std::mutex, std::recursive_mutex, std::timed_mutex, std::recursive_timed_mutex. Section 30.4.1, Intransitive if you supply your own exception free locking (via BasicLockable, Lockable, TimedLockable). Abstraction implemented using native implementations.
std::condition_variable Section 30.5. Transitive. Abstraction implemented using native implementations.
note: There will be more.
I always end up using my own minimalistic wrapper for JSON-RPC (because it's trivially simple): am I missing out on something compared to standard libraries?
Yes it's simple. In past I took similar approach as yours and had my own minimal json-rpc implementation. Now I use jsonrpc2 for a fairly complex application. What I was missing earlier
Didn't have batched call support
All error code supported
better tested library
more goodies like rpc processor (check jsonrpc2's documentation)
other obvious advantages of open source :-)
If your looking for a .net jsonrpc2 server. Check out http://jsonrpc2.codeplex.com/
I would also add to Shekhar's list
Speed of development by skipping the 'roll your own' step.
Cost - is most cost effective to use a library supported by the community.
Its likely better tested, and more stable then a roll your own solution.
Performance of the json-rpc server is likely better then you would get with a roll your own solution.
** maintainability ** There is documentation around Json-Rpc 2. Another developer will be able to contribute on your project or fix bugs better if the protocol has a defined spec. They may be familiar with it already.
In the case of Json-Rpc.net, to make a method a json-rpc method, all you have to do is add an attribute to the method. So another plus for using a real json-rpc implementation.
Background
The book The Joy of Clojure explains how JVM exceptions are a closed system and suggests that there may be better alternatives for reporting and handling errors in clojure. From my experience, the common lisp condition system seems ideal, however, I am not restricting answers to this paradigm. From what I've researched there are conditions (Gilardi) http://clojure.github.com/clojure-contrib/condition-api.html , error-kit (Chouser) http://richhickey.github.com/clojure-contrib/error-kit-api.html, and handler (Weiss) https://gist.github.com/745223, however there does not appear to be a clear winner among these implementations and I feel more information on topic would be useful.
How have existing alternatives been successfully used in projects? I'm looking for examples to emulate.
How do these alternative systems overcome limitations with the JVM exception system?
What are the future directions or what are experimental alternatives on the horizon and what they entail?
FYI, this is being discussed in clojure-dev. Ideas collecting here and thread here.
Many years have passed since the question was asked, but I think the topic is still relevant. I have been working on Promenade (see documentation) that can express error as data and provides elegant error handling and control flow. There are also other projects (mentioned on Promenade README) trying to address the same issue.