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
I had a rapid look; unfortunately not in sufficient details to
grasp the major departures from the existing framework.
Could you display one or two examples comparing CM and firefly?
In addition to what I summarized below one detail that I think is
important is that the ExceptionTypes enum allows for more exact
targeting of the exception root cause. For instance right now I have
the following arithmetic exception types:
/**
* MATH ARITHMETIC EXCEPTIONS
*/
MAE("MAE"),
MAE__INTEGER_OVERFLOW("MAE__INTEGER_OVERFLOW"),
MAE__LONG_OVERFLOW("MAE__LONG_OVERFLOW"),
MAE__OVERFLOW_IN_ADDITION("MAE__OVERFLOW_IN_ADDITION"),
MAE__OVERFLOW_IN_SUBTRACTION("MAE__OVERFLOW_IN_SUBTRACTION"),
MAE__GCD_OVERFLOW_32_BITS("MAE__GCD_OVERFLOW_32_BITS"),
MAE__GCD_OVERFLOW_64_BITS("MAE__GCD_OVERFLOW_64_BITS"),
MAE__LCM_OVERFLOW_32_BITS("MAE__LCM_OVERFLOW_32_BITS"),
MAE__LCM_OVERFLOW_64_BITS("MAE__LCM_OVERFLOW_64_BITS"),
MAE__DIVISION_BY_ZERO("MAE__DIVISION_BY_ZERO"),
Side remark: The argument to the enum element is the same as the enum
element's name; is there a way to avoid the duplication (i.e. the string
would be generated automatically)?
Good point! Originally I was considering using numbers for each group of
exceptions. For example 100 for arithmetic exceptions, 200 for matrix
exceptions, etc. But I think strings are fine. So now it's down to this:
https://github.com/firefly-math/firefly-math-exceptions/blob/master/src/main/java/com/fireflysemantics/math/exception/ExceptionTypes.java
/**
* MATH ARITHMETIC EXCEPTIONS
*/
MAE,
MAE__INTEGER_OVERFLOW,
MAE__LONG_OVERFLOW,
MAE__OVERFLOW_IN_ADDITION,
MAE__OVERFLOW_IN_SUBTRACTION,
MAE__GCD_OVERFLOW_32_BITS,
MAE__GCD_OVERFLOW_64_BITS,
MAE__LCM_OVERFLOW_32_BITS,
MAE__LCM_OVERFLOW_64_BITS,
MAE__DIVISION_BY_ZERO,
...
So by looking at the exception type we know exactly what the issue
is.
With this approach CM will always only have 1 exception. If more
types are needed then just add another line to the ExceptionTypes
Enum. The new type is used to look up the message template in the
I18N resource bundle.
It looks neat.
Thanks :)
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 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 :).
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.
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.
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.
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?
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();
Cheers,
Ole
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