RFR 8135248: Add utility methods to check indexes and ranges

Paul Sandoz paul.sandoz at oracle.com
Tue Sep 22 08:09:56 UTC 2015

Hi Remi,

On 22 Sep 2015, at 08:08, Remi Forax <forax at univ-mlv.fr> wrote:
> Hi  Paul,
> to summarize, there are a lot of codes that do bound checking in the JDK that report different kind of exceptions.

Yes, and I suspect it is a similar state of affairs for code outside of the JDK too.

> A way to retrofit most of then is to use a lambda to let the user code to choose its convention.
> But because lambda creations are backed by invokedynamic, you can not retrofit
> code that is used before the method handle mechanism is set up during the bootstraping of the JDK.

We can retrofit, but we will not use lambda expressions or method refs in those cases.

> There are several kinds of bound checking, and i see no gain to force them to use the same function type.
> Also, I have use a wildcard instead of a type variable given that it's an unchecked exception for the compiler.
> For the simplest form of bound checking, 0 <= index < length, aka checkIndex, because there is only one index to report, i propose:
>  public static void checkIndex(int index, int length, IntFunction<? extends RuntimeException> exceptionCreator)

I disagree, we need BiFunction. I have eyeballed a sufficient number of use-cases that report index and length in the exception message.

> For the form of that uses a size, 0 <= index < size <= length, aka checkFromIndexSize, as you said, let's use a BiFunction<Integer, Integer, ...>,
>  public static void checkRange(int index, int size, int length, BiFunction<Integer, Integer, ? extends RuntimeException> exceptionCreator)
> For the form that uses an offset, 0 <= index <= index + offset < length,
>   public static void checkRangeWithOffset(int index, int offset, int length, BiFunction<Integer, Integer, ? extends RuntimeException> exceptionCreator)
> Also, the documentation should be clear that if a lambda captures values from the context, the performance will be worst than inlining the check by hand.

Yes, i can write some api note. FWIW for the sub-range checks it probably matters less as those are often followed by some bulk operation.


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