RFR: 8303882: Refactor some iterators in jdk.compiler [v3]

[Maurizio Cimadamore]

On Mon, 13 Mar 2023 10:43:04 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Pavel Rappo has updated the pull request incrementally with four additional commits since the last revision:
>> 
>>  - Merge remote-tracking branch 'myjdk/8303882' into 8303882
>>  - Squeeze a few extra drops of perf
>>  - Add a recursive test
>>  - Try squeeze more performance
>
> test/langtools/tools/javac/util/IteratorsTest.java line 163:
> 
>> 161: 
>> 162:         public TestConverter(Function<I, Iterator<O>> delegate) {
>> 163:             this.delegate = delegate;
> 
> This parameter doesn't really seem to be used in the test?

I suggest this TestConverter to take a single type parameter `T` and implement `Function<TestIterator<S>, Iterator<S>>`

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PR: https://git.openjdk.org/jdk/pull/12949