RFR: 8305774: String.join(CharSequence, Iterable) can be optimized if Iterable is a Collection [v2]

[Glavo]

On Mon, 10 Apr 2023 05:14:16 GMT, Glavo <duke at openjdk.org> wrote:

>> @Glavo Then why doesn't `ArrayList` trust `toArray()`? If all implementations behave correctly, then it should return an `Object[]` independent of the original collection, so `ArrayList` should trust it. Those who doesn't implement `toArray()` correctly should use these methods at their own risk, shouldn't they?
>> 
>> This PR modifies a class that is used by nearly every JVM code, so safety is more important than performance.
>
> @yuantj As I mentioned earlier, we need to prevent errors from leaking to other places, rather than defending against all errors.

> @Glavo Then why doesn't `ArrayList` trust `toArray()`? If all implementations behave correctly, then it should return an `Object[]` independent of the original collection, so `ArrayList` should trust it. Those who doesn't implement `toArray()` correctly should use these methods at their own risk, shouldn't they?

I already explained the reason in detail in my earliest reply.

> This PR modifies a class that is used by nearly every JVM code, so safety is more important than performance.

Even without using `toArray`, security cannot be guaranteed. Just like the `BadList` in my previous example, if you cannot trust this collection, then we cannot do anything because its iterator may also be unsafe.

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PR Comment: https://git.openjdk.org/jdk/pull/13383#issuecomment-1501408139