Le 24/12/2015 14:13, Gilles a écrit :
> On Thu, 24 Dec 2015 09:36:34 +0100, Luc Maisonobe wrote:
>> Le 24/12/2015 01:41, Gilles a écrit :
>>> On Wed, 23 Dec 2015 20:18:10 +0100, Luc Maisonobe wrote:
>>>> Le 23/12/2015 14:32, Gilles a écrit :
>>>>> Hello.
>>>>>
>>>>> On Wed, 23 Dec 2015 10:38:03 +0100, luc wrote:
>>>>>> Le 2015-12-23 01:41, Gilles a écrit :
>>>>>>> On Tue, 22 Dec 2015 13:17:16 -0600, Ole Ersoy wrote:
>>>>>>>> On 12/22/2015 11:46 AM, Gilles wrote:
>>>>>>>>> Hi.
>>>>>>>>> On Mon, 21 Dec 2015 22:44:16 -0600, Ole Ersoy wrote:
>>>>>>>>>> On 12/21/2015 06:44 PM, Gilles wrote:
>>>>>>>>>>> On Mon, 21 Dec 2015 12:14:16 -0600, Ole Ersoy wrote:
>>>>>>>>>>>> Hi,
>>>>>>>>>>>> I was considering jumping into the JDKRandomGenerator exception
>>>>>>>>>>>> discussion, but I did not want to hijack it.
>>>>>>>>>>>> Not sure if any of you have had a chance to looks at this:
>>>>>>>>>>>> https://github.com/firefly-math/firefly-math-exceptions/
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> https://github.com/firefly-math/firefly-math-exceptions/blob/master/src/main/java/com/fireflysemantics/math/exception/MathException.java
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>> [...]
>>>>>>>>>>> But I did not see how localization is handled.
>>>>>>>>>> I did leave localization out. I think localization was a hard
>>>>>>>>>> requirement in earlier versions of CM, but I'm hoping that
>>>>>>>>>> there is
>>>>>>>>>> some flexibility on this
>>>>>>>>> There was not, since I argued many times to leave it out.
>>>>>>>>> So unless you can show practically how it can work, I have my
>>>>>>>>> doubts
>>>>>>>>> that we'll be allowed to go forward with this approach.
>>>>>>>>>
>>>>>>>>>> and that future versions can defer to a
>>>>>>>>>> utility that uses the ExceptionTypes Enum instance as the key to
>>>>>>>>>> look
>>>>>>>>>> up the internationalized template string.
>>>>>>>>> Looks good. Where is the code? ;-)
>>>>>>>> So CM clients would:
>>>>>>>> catch(MathException e) {
>>>>>>>> String exceptionTemplate =
>>>>>>>> ResourceBundle.getBundle("cm.exception.templates", new Locale("en",
>>>>>>>> "US")).getString(e.getType());
>>>>>>>> String i18Nmessage = buildMessage(exceptionTemplate,
>>>>>>>> e.getContext());
>>>>>>>> ...
>>>>>>>> }
>>>>>>>> I can prototype that out more. Just trying to get a feel for how
>>>>>>>> viable the concept is first.
>>>>>>> I'm not sure I understand correctly.
>>>>>>> Does that mean that
>>>>>>> 1. Uncaught exceptions will lead to a message in English?
>>>>>>> 2. Every "catch" must repeat the same calls (although the arguments
>>>>>>> are likely
>>>>>>> to be the same for all clauses (and for all applications)?
>>>>>>> Comparing this with the current behaviour (where the translated
>>>>>>> message String
>>>>>>> is created when "e.getLocalizedMessage()" is called) is likely to
>>>>>>> make people
>>>>>>> unhappy.
>>>>>>
>>>>>> This could be made simpler with some task delegating between user
>>>>>> code and CM code.
>>>>>> What about :
>>>>>>
>>>>>> interface ExceptionLocalizer {
>>>>>> /** Localize an exception message.
>>>>>> * @param locale locale to use
>>>>>> * @param me exception to localize
>>>>>> * @return localized message for the exception
>>>>>> */
>>>>>> String localize(Locale locale, MathException me);
>>>>>> }
>>>>>>
>>>>>> and having ExceptionFactory hold a user-provided implementation of
>>>>>> this interface?
>>>>>>
>>>>>> public class ExceptionFactory {
>>>>>>
>>>>>> private static ExceptionLocalizer localizer = new NoOpLocalizer();
>>>>>>
>>>>>> public static setLocalizer(ExceptionLocalizer l) {
>>>>>> localizer = l;
>>>>>> }
>>>>>
>>>>> I think that this is potentially dangerous for two reasons (if I'm
>>>>> not mistaken): it's not thread-safe and it can be called by any
>>>>> library used by the main application.
>>>>
>>>> Intermedaite libraries could also call it, and I hope they would be
>>>> designed to use a consistent way for their own exception (they should
>>>> let the user specify the localization mechanism, use it for themselves
>>>> and pass the configuration to CM).
>>>
>>> I'm not sure I follow.
>>>
>>> IIUC the implications, libraries should be forbidden to call a method
>>> such as "setLocalizer".
>>
>> It's a design choice for the upper libraries, not for CM.
>
> Not for upper libraries, only for the user!
>
> Anyway, the design choice at CM level is: localization or not?
>
> My opinion is that a low-level component should not do localization.
>
> If the exception is a programming error, it is a bug (bad input
> provided by the caller).
> When something like that is encountered, the stack trace must be
> reported to the caller of the method that triggered the exception
> (either application developer, or CM developer).
> I'm sure that a localized detailed message is a nuisance to the
> people who have to debug (what if we provided e.g. Chinese
> translations?).
>
> If people feel that an operator cannot see a CM message in English
> on his console, what do they do to prevent the JVM to show them?
>
> For the few cases in CM that cannot be safe-guarded by precondition
> checks, it's less clear-cut.
> But I still think that localization is a job for a wrapper.
> I.e. if CM would throw an exception instance whose type is a one-to-one
> mapping to a cause, the wrapper has all the info to make a full report
> (in any language).
>
>>>>
>>>> Thread safety here is really not a concern (but we could protect it
>>>> if desired). This setting is a configuration level setting, it is
>>>> usually done once near the beginning of the main program. You don't
>>>> change the mechanism every millisecond.
>>>>
>>>>>
>>>>> I think that the "localizer" instance must be obtained in a way which
>>>>> the end-user controls.
>>>>
>>>> The user controls it. The setLocalizer method can be called directly by
>>>> user, and in fact I expect the user to do it.
>>>
>>> The user is not in control because any code he calls can override the
>>> setting.
>>>
>>>>>>
>>>>>> public static String localize(Locale locale, MathException me) {
>>>>>> return localizer.localize(locale, me);
>>>>>> }
>>>>>>
>>>>>> /** Default implementation of the localizer that does nothing. */
>>>>>> private static class NoOpLocalizer implements ExceptionLocalizer {
>>>>>> /** {@inheritDoc} */
>>>>>> @Override
>>>>>> public String localize(MathException me) {
>>>>>> return me.getMessage();
>>>>>> }
>>>>>> }
>>>>>>
>>>>>> }
>>>>>>
>>>>>> and MathException could implement both getLocalizedMessage() and
>>>>>> even getMessage(Locale) by delegating to the user code:
>>>>>>
>>>>>> public class MathException {
>>>>>>
>>>>>> public String getLocalizedMessage() {
>>>>>> return ExceptionFactory.localize(Locale.getDefault(), this);
>>>>>> }
>>>>>>
>>>>>> public String getMessage(Locale locale) {
>>>>>> return ExceptionFactory.localize(locale, this);
>>>>>> }
>>>>>>
>>>>>> ...
>>>>>>
>>>>>> }
>>>>>>
>>>>>> One thing that would be nice would be that in addition to the get
>>>>>> method,
>>>>>> MathException also provides a getKeys to retrieve all keys and a
>>>>>> getType
>>>>>> to retrieve the type. The later correspond to the getPatern (or
>>>>>> getLocalizable)
>>>>>> I asked for a few years ago in ExceptionContext. The point for these
>>>>>> methods
>>>>>> is that if we provide users a way to retrieve the parameters that
>>>>>> were
>>>>>> used
>>>>>> in the exception construction, then we can delegate localization to
>>>>>> users
>>>>>> as they can do their own code that will rebuild a complete
>>>>>> meaasage as
>>>>>> they
>>>>>> want. When you have only the keys and they have reused names like
>>>>>> OPERATOR
>>>>>> or VECTOR, it can't be delegated.
>>>>>
>>>>> If those are available (as suggested in Ole's example above), would
>>>>> you
>>>>> indeed
>>>>> be OK that localization is not a CM concern anymore?
>>>>
>>>> Yes at the condition that user can use it to implement something like
>>>> the ExceptionLocalizer interface and this interface is already
>>>> supported
>>>> by CM exceptions to implement getLocalizedMessage (at least). The
>>>> getLocalizedMessage is a standard method inherited directly from
>>>> Throwable, it is not an addition from us (on the other hand
>>>> getMessage(Locale) *is* an extension I promoted).
>>>
>>> I don't follow: I thought that if Ole's "MathException" provides
>>> "getType",
>>> "getKeys" and ("getValues" ?), then you have the same building blocks
>>> to define a custom formatting (and localization).
>>
>> Yes, and this is what is used at user level to implement
>> ExceptionLocalizer.
>
> But it is also enough for the wrapper (see above) to do its job.
>
>>>
>>> By "dropping support", I mean dropping support. ;-)
>>> I.e. no more "Localize..." classes under "org.apache.commons.math4"
>>
>> Then -1.
>>
>> When our users build a large application, they rely on numerous
>> different libraries and tools, both open-source and proprietary.
>> These libraries do have standard interfaces so they can be used
>> together. The Java standard library is one of them. the
>> getLocalizedMessage method is specified there. Many of the libraries
>> and tolls user will assemble rely on it. Deciding that for the sake
>> of Apache Commons Math we do not abide to this and decide that all
>> other existing code should adapt to a different design is a clear
>> no go for me.
>
> Does the JVM abide by this?
Yes, as well as JUnit, Eclipse, Maven, and all tools I use.
>
> The point is that CM code is not user-level code: requirements that
> have nothing to do with mathematical algorithms should not have
> top-level priority here. This is what has always biased this
> discussion.
>
> This issue is not one of a design that would not use "getLocalizedMessage"
> just that CM is not the place to do so. CM throws exception; caller
> handle them in any way they want.
> For example:
>
> try {
> // ...
>
> // Use a low-level library: do not let foreign exceptions bubble up.
> try {
> CMAlgo algo = new CMAlgo();
> algo.run();
> } catch(RuntimeException e) {
> if (e instanceof CMAlgoException)
> throw new MyCMAlgoException(e);
> } else {
> throw new MyUnexpectedException(e);
> }
> }
>
> // ...
> } catch (MyRuntimeException e) {
> LOG.error(e.getLocalizedMessage()); //
> }
Times thousands times as CM call in complex applications that do
a lot of math occur everywhere.
>
>> Look at it, it is *only* one field with its setter and two one line
>> methods defined in the top level MathException class in order to
>> abide to a standardized interface widely used.
>
> OK, and I also worked a lot to make it less of a duplication mess.
> I don't think that I can oppose you on these 3 lines given all the
> work you do. ;-)
Thanks.
>
> But once and for all, I'd like that we acknowledge that this decision
> has nothing to do with good design.
I don't claim this to be good design. It is only meant to be practical
and not cumbersome for users.
>
>>>
>>> The list of translated type could still be maintained here, in the same
>>> way the unit tests and user guide are.
>>
>> I'm not sure. If we decide to delegate the localization to the user
>> and simply provide the two one-liners hook to call it, then we can
>> remove the list of translated types and let the user handle it. It
>> would also allow them to support additional languages. For now,
>> we support only one, we could drop it using this delegation mechanism.
>
> I just meant it as a service to the international of users. :-)
> We could centralize the translations as is done for other resources like
> the userguide.
This is fine with me.
>
>>
>>>
>>>> This getLocalizedMessage is the standard way many existing frameworks
>>>> use to display the message to end users, and we can't change this
>>>> behaviour to have them call the user localization code. So this user
>>>> localization code must lie somewhere beneath the standard
>>>> getLocalizedMessage call. The proposal above allow to divert it to
>>>> user code with CM providing only the required plumbing (but it must
>>>> still provide the plumbing).
>>>>
>>>>>
>>>>> We could provide code of how to perform the translation in the
>>>>> userguide.
>>>>
>>>> Yes.
>>>>
>>>>>
>>>>>> Note that this is independent of the fact there is one or several
>>>>>> hierarchies.
>>>>>> If there are several ones, the two one-liners above must simply be
>>>>>> copied
>>>>>> (yeah, code duplication, I know).
>>>>>>
>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>> I think it satisfies everyone's requirements with:
>>>>>>>>>>>> - A single MathException (No hierarchy)
>>>>>>>>>>> That would not satisfy everyone. :-!
>>>>>>>>>>>
>>>>>>>>>>>> - The ExceptionTypes Enum contains all the exception types
>>>>>>>>>>>> - The ExceptionTypes Enum 'key' maps to the corresponding
>>>>>>>>>>>> message 1 to 1
>>>>>>>>>>>> - The ExceptionFactory (Utility) throws exceptions, if
>>>>>>>>>>>> necessary,
>>>>>>>>>>>> that have always have a single unique root cause, such as NPEs
>>>>>>>>>>> I was wondering whether the "factory" idea could indeed satisfy
>>>>>>>>>>> everyone.
>>>>>>>>>>> Rather than throwing the non-standard "MathException", the
>>>>>>>>>>> factory would
>>>>>>>>>>> generate one of the standard exceptions, constructed with the
>>>>>>>>>>> internal
>>>>>>>>>>> "MathException" as its cause:
>>>>>>>>>> I think it's good that CM throws CM specific exceptions. This
>>>>>>>>>> way
>>>>>>>>>> when I write the handler I can know that the exception is CM
>>>>>>>>>> specific
>>>>>>>>>> without having to unwrap it.
>>>>>>>>> But if there are several CM exceptions hierarchies, the handler
>>>>>>>>> will have
>>>>>>>>> to check for every base type, leading to more code.
>>>>>>>> True dat - but if there are no CM exception hierarchies then they
>>>>>>>> don't :).
>>>>>>> I'd be interested in settling the matter of whether we must use a
>>>>>>> single
>>>>>>> hierarchy because of technical limitations, or if it is a good
>>>>>>> solution
>>>>>>> on its own, i.e. extending standard exceptions is not a better
>>>>>>> practice
>>>>>>> after all.
>>>>>>>
>>>>>>>>> We could provide a utility:
>>>>>>>>> public boolean isMathException(RuntimeException e) {
>>>>>>>>> if (e instanceof MathException) {
>>>>>>>>> return true;
>>>>>>>>> }
>>>>>>>>> final Throwable t = e.getCause();
>>>>>>>>> if (t != null) {
>>>>>>>>> if (e instanceof MathException) {
>>>>>>>>> return true;
>>>>>>>>> }
>>>>>>>>> }
>>>>>>>>> return false;
>>>>>>>>> }
>>>>>>>> Or just not wrap.
>>>>>>> Of course, but choosing one or the other is not a technical problem;
>>>>>>> it's design decision. Do we have arguments (or reference to them)?
>>>>>>>
>>>>>>>>>>> public class ExceptionFactory {
>>>>>>>>>>> public static void throwIllegalArgumentException(MathException
>>>>>>>>>>> e) {
>>>>>>>>>>> throw new IllegalArgumentException(e);
>>>>>>>>>>> }
>>>>>>>>>>> public static void throwNullPointerException(MathException e) {
>>>>>>>>>>> throw new NullPointerException(e);
>>>>>>>>>>> }
>>>>>>>>>>> // And so on...
>>>>>>>>>>> }
>>>>>>>>>>> So, CM code would be
>>>>>>>>>>> public class Algo {
>>>>>>>>>>> public void evaluate(double value) {
>>>>>>>>>>> // Check precondition.
>>>>>>>>>>> final double min = computeMin();
>>>>>>>>>>> if (value < min) {
>>>>>>>>>>> final MathException e = new
>>>>>>>>>>> MathException(NUMBER_TOO_SMALL).put(CONSTRAINT, min).put(VALUE,
>>>>>>>>>>> value);
>>>>>>>>>>> ExceptionFactory.throwIllegalArgumentException(e);
>>>>>>>>>>> }
>>>>>>>>>>> // Precondition OK.
>>>>>>>>>>> }
>>>>>>>>>>> }
>>>>>>>>>> Another thing that I hinted to is that the the factory builds in
>>>>>>>>>> the
>>>>>>>>>> precondition check in the throw method. So that the line:
>>>>>>>>>> if (value < min) {
>>>>>>>>>> can be nixed.
>>>>>>>>> It seems nice to ensure that the exception raised is consistent
>>>>>>>>> with the
>>>>>>>>> checked condition.
>>>>>>>> That's the idea.
>>>>>>> OK, but do you foresee that all precondition checks will be
>>>>>>> handle by
>>>>>>> factory methods.
>>>>>>> It would not be so nice to have explicit checks sprinkled here and
>>>>>>> there.
>>>>>>>
>>>>>>>>> Then, a factory method like
>>>>>>>>> throwNotStrictlyPositiveException(Number value, String key)
>>>>>>>>> should probably be renamed to
>>>>>>>>> checkNotStrictlyPositiveException(Number value, String key)
>>>>>>>> 'check' is good. I'm going to change it to check.
>>>>>>
>>>>>> as the name was changed to checkSomething, the last part Exception in
>>>>>> the name could be dropped.
>>>>>>
>>>>>>>>> Also, shouldn't the "key" argument should be optional?
>>>>>>>> The key is used to initialize the exception context with the Number
>>>>>>>> instance. Different modules could have different keys. For
>>>>>>>> example
>>>>>>>> the Arithmetic module has keys X and Y. So if Y caused the
>>>>>>>> exception
>>>>>>>> then Y would be passed as the key. So if we are checking both we
>>>>>>>> would do this:
>>>>>>>> checkNotStrictlyPositiveException(x, X);
>>>>>>>> checkNotStrictlyPositiveException(y, Y);
>>>>>>>>>
>>>>>>>>>>> Then, in an application's code:
>>>>>>>>>>> public void appMethod() {
>>>>>>>>>>> // ...
>>>>>>>>>>> // Use CM.
>>>>>>>>>>> try {
>>>>>>>>>>> Algo a = new Algo();
>>>>>>>>>>> a.evaluate(2);
>>>>>>>>>>> } catch (IllegalArgumentException iae) {
>>>>>>>>>>> final Throwable cause = iae.getCause();
>>>>>>>>>>> if (cause instanceof MathException) {
>>>>>>>>>>> final MathException e = (MathException) cause;
>>>>>>>>>>> // Rethrow an application-specific exception that will make more
>>>>>>>>>>> sense
>>>>>>>>>>> // to my customers.
>>>>>>>>>>> throw new InvalidDataInputException(e.get(CONSTRAINT),
>>>>>>>>>>> e.get(VALUE));
>>>>>>>>>>> }
>>>>>>>>>>> }
>>>>>>>>>>> }
>>>>>>>>>>> This is all untested.
>>>>>>>>>>> Did I miss something?
>>>>>>
>>>>>> In the code above, if the iae does not have a cause, or if it is not
>>>>>> a MathException,
>>>>>> the iae should be rethrown.
>>>>>
>>>>> Indeed!
>>>>> The updated code (also unstested):
>>>>>
>>>>> try {
>>>>> Algo a = new Algo();
>>>>> a.evaluate(2);
>>>>> } catch (IllegalArgumentException iae) {
>>>>> final MathException e = ExceptionFactory.getMathException(iae);
>>>>>
>>>>> if (e != null) {
>>>>> // Rethrow an application-specific exception that will make
>>>>> more
>>>>> sense
>>>>> // to my customers.
>>>>> throw new InvalidDataInputException(e.get(CONSTRAINT),
>>>>> e.get(VALUE));
>>>>> } else {
>>>>> throw iae;
>>>>> }
>>>>> }
>>>>>
>>>>>>>>>> I think you got it all...But the handler will be shorter if the
>>>>>>>>>> exception is not wrapped.
>>>>>>>>> But not significantly, I guess.
>>>>>>>>> We could also provide
>>>>>>>>> public MathException getMathException(RuntimeException e) {
>>>>>>>>> if (e instanceof MathException) {
>>>>>>>>> return (MathException) e;
>>>>>>>>> }
>>>>>>>>> final Throwable t = e.getCause();
>>>>>>>>> if (t != null) {
>>>>>>>>> if (e instanceof MathException) {
>>>>>>>>> return (MathException) e;
>>>>>>>>> }
>>>>>>>>> }
>>>>>>>>> return null;
>>>>>>>>> }
>>>>>>>>> And then define the other utility as:
>>>>>>>>> public boolean isMathException(RuntimeException e) {
>>>>>>>>> return getMathException(e) != null;
>>>>>>>>> }
>>>>>>>>>
>>>>>>>>>> The pattern I'm used to is that libraries
>>>>>>>>>> wrap the exceptions of other libraries in order to offer a
>>>>>>>>>> standardized facade to the user. For example Spring wraps
>>>>>>>>>> Hibernate
>>>>>>>>>> exceptions, since Spring is a layer on top of Hibernate and other
>>>>>>>>>> data
>>>>>>>>>> access providers.
>>>>>>>>> What do they advertize? Standard exception, possibly extended, or
>>>>>>>>> specific ones, possibly belonging to single hierarchy?
>>>>>>>> Spring namespaced - single hierarchy:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/dao/DataAccessException.html
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> BTW - this is blue sky thinking - but Spring Boot has an
>>>>>>>> @ExceptionHandler annotation that allows the developer to wire
>>>>>>>> up an
>>>>>>>> exception handler. It might be worth exploring something
>>>>>>>> similar for
>>>>>>>> the purpose of automating I18N requirements.
>>>>>>>> @ExceptionHandler(MathException.class)
>>>>>>>> someClientCodeThatUsesCM();
>>>>>>>
>>>>>>> That would be quite necessary I'm afraid. ;-)
>>>>>>
>>>>>> Not necessarily. The above support for I18N is quite simple.
>>>>>
>>>>> Maybe too simple... ;-)
>>>>> [What did they say about global variables?]
>>>>
>>>> If the static fields hurts your feelings,
>>>
>>> It's not just that.
>>>
>>>> we can always hide
>>>> it using an official design pattern like the singleton for
>>>> ExceptionFactory, and even use the Initialization-on-demand
>>>> holder idiom to store the singleton. Then the localizer would
>>>> be an instance field and there would be a static getInstance()
>>>> method in the factory. Well, a singleton design pattern plus
>>>> a IODH idiom design pattern are really only a global variable
>>>> in a pretty dress, so it is only hiding the fact.
>>>
>>> Unless I'm mistaken, other singletons in CM are initialized by CM,
>>> and cannot be changed afterwards.
>>>
>>>> At the root, yes global variables are frowned upon, but they
>>>> do have some use for configuration and making sure some
>>>> configuration data can be retrieved from everywhere reliably.
>>>> There are many other places were global variables are used in
>>>> Java. Just to mention one example that is deirectly related
>>>> to our topic, Locale.getDefault() and Locale.setDefault() are
>>>> semantically really accesses to a global variable too.
>>>
>>> I think that this is not something to introduce lightly.
>>> When/if we'll want to explore multi-threading, it will add to
>>> the problems.
>>
>> I don't agree at all with this statement.
>>
>> This is a configuration setting, expected to be called once
>> at start time! I cannot see any case with users attempting
>> to do it hundreds of time per seconds with different localizers
>> to handle localization. This can be documented and users can be
>> warned against.
>>
>> What I do expect is, in cases of server applications, having
>> a server answering to remote requests using different languages.
>> This is what the new getMessage(Locale) is designed for. Here,
>> the locale changes, not the mechanism to support it, and it
>> is not a global variable, just a method argument. It is already
>> safe in multi-threaded environments.
>>
>> The setLocalizer method is not a computation algorithm expected
>> to be called millions of times and that therefore could experience
>> clashes in case of concurrency.
>
> I was not considering this case.
> Just the inherent potential problem of a global setter for a
> low-level library.
> Do you know of other libraries that do such a thing?
At least Orekit (for something called DataProvidersManager, which
is a singleton and uses initialization-on-demand holder idiom),
but this example is biased ;-)
Another example would be log4j2, with the MainMapLookup singleton
and its setMainArguments method that is intended to be called once
with the main arguments, but nothing prevents it to be called
at will (and there are no protections against concurrent accesses).
There is also the JSCH library which uses a private static map for
config and has setters and getters allowing to change its content
(here, there are some protections agains concurrent access).
In many case, as long as you need to store some configuration,
you end up with either a static field (often private and
with getters/setters) or an instance field in a singleton.
It happens in the best libraries.
best regards,
Luc
>
> Thanks,
> Gilles
>
>>
>> best regards,
>> Luc
>>
>>> If the localization feature can be achieved without resorting
>>> to a global setting, we should favour it.
>>>
>>> Best,
>>> Gilles
>>>
>>>>
>>>> best regards,
>>>> Luc
>>>>
>>>>>
>>>>> Best regards,
>>>>> Gilles
>>>>>
>>>>>>
>>>>>> best regards,
>>>>>> Luc
>>>>>>
>>>>>>> Best regards,
>>>>>>> Gilles
>>>>>>>
>>>>>>>> Cheers,
>>>>>>>> Ole
>
>
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