[design] indexing into enums / enum.indices

bradcray · November 8, 2021, 6:49pm

Hi Chapel community —

I'm looking for feedback on a proposal to support two new features on enum types:

supporting myEnum[i] as a means of getting the 'i'th symbol in the enumeration
supporting myEnum.indices as a means of getting the range 0..<myEnum.size

The first supplies a capability that is not available for end-users today; the second continues the recent trend of having indexable things support a query indicating what indices can be used with them.

If you have thoughts on this, or would like to upvote the proposal, please see:

github.com/chapel-lang/chapel

Should enums support `.indices` and indexing?

opened 11:11PM - 05 Mar 20 UTC

bradcray

Internally, Chapel uses a dense indexing scheme for enum symbols that is used to… store and track them. Conversions between the indices and enum symbols and back again have been supported by undocumented routines and are useful when doing things like I/O or using implementing ranges of enums. This issue asks whether these indices should be exposed more directly to users as well. For example, imagine: * `proc type enum.indices`: would return the legal set of indices for accessing an enum (say 0..#enum.size) * `proc type enum.this(i: integral)`: would return the i-th constant in the enumeration Thus: ```chapel enum color = {red, green, blue}; writeln(color.indices); // would write out `0..2` writeln(color(1)); // would write out `green` ```

Thanks,
-Brad

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[design] indexing into enums / enum.indices

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