8257466: Improve enum iteration

[kimbarrett]

Please review this collection of improvements to the recently added enum
iteration facility. These improvements are based on usage in some
in-development changes.

(1) Added EnumType nested type to EnumRange and EnumIterator. It is an alias
for the enum type that is a template parameter for those classes. This is
useful when dealing with a range or iterator whose associated enum type is
not known because the range/iterator is a template parameter.

(2) Added EnumRange::index(T), which converts the argument enumerator to
a zero-based index into the range of values. This is useful when mapping
from an enumerator to a corresponding array index, for example.

(3) Allow enum range bounds to be specified using start and (exclusive) end
integral (underlying type) values. This is useful when dealing with enums
that are just value ranges and don't have named enumerators. As part of
this, changes the enum iteration traits mechanism to use start/end rather
than first/last, as that seems to be a little easier to deal with.

(4) Added accessors for the first and last enumerator values of a range.

(5) Added gtest for enum iteration.

Testing: tier1

/label hotspot

---

Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change must be properly reviewed

Issue

• JDK-8257466: Improve enum iteration

Reviewers

• Ioi Lam (@iklam - Reviewer) ⚠️ Review applies to 6911c0f
• Lois Foltan (@lfoltan - Reviewer) ⚠️ Review applies to 6911c0f

Download

$ git fetch https://git.openjdk.java.net/jdk pull/1530/head:pull/1530
$ git checkout pull/1530

[bridgekeeper]

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[openjdk]

@kimbarrett
The hotspot label was successfully added.

[mlbridge]

Webrevs

• 02: Full - Incremental (ef12da9)
• 01: Full - Incremental (6911c0f)
• 00: Full (3a4dbd5)

[iklam]

Why do we need to call underlying<T>(Start) here? Can it be simplified as

static constexpr EnumeratorRangeImpl::Underlying<T> _start = Start;

or

static constexpr EnumeratorRangeImpl::Underlying<T> _start {Start};

[kimbarrett]

I'd earlier considered requiring the type of Start and End be Underlying rather than convertible to that. The underlying() function is a partial remnant of that. I'll remove it.

[kimbarrett]

Using brace initialization is the way to go, as it prevents narrowing.

[openjdk]

@kimbarrett This change now passes all automated pre-integration checks.

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After integration, the commit message for the final commit will be:

8257466: Improve enum iteration

Improve support for iteration on enums that are just range of values, without named enumerators.

Reviewed-by: iklam, lfoltan

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

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[lfoltan]

Changes looks good Kim.
Lois

[kimbarrett]

Thanks for reviewing @iklam and @lfoltan

[kimbarrett]

/summary Improve support for enums that are just range of values, without named enumerators.

[openjdk]

@kimbarrett Setting summary to Improve support for enums that are just range of values, without named enumerators.

[kimbarrett]

/summary Improve support for iteration on enums that are just range of values, without named enumerators.

[openjdk]

@kimbarrett Updating existing summary to Improve support for iteration on enums that are just range of values, without named enumerators.

[kimbarrett]

/integrate

[openjdk]

@kimbarrett Pushed as commit 3932527.

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