Iterate over default's field variants in enums

[LafCorentin]

Hi

I needed to iterate over en enum's default variant, so I added a option to enum-iterator.

If you prefer other terms or structure I would be glad to adapt.

All tests are good.

[stephaneyfx]

Hi @LafCorentin,

Thank you for opening this PR and I apologize for the late response.

May you share your concrete use case where only default values are needed for variants with fields?

Does that do what you want?

[LafCorentin]

This is about representing a menu. the value is changed for the previous or following one, cycling both way. With your crate I have the cardinal of the the enum sizing my menu, access to the last one to cycle in reverse, and it can iterate both way endlessly without consuming anything. I don't feel like the other iterator is made for that.
But yeah I'm bringing their approach with my option.

[stephaneyfx]

Let's assume that the menu represents the Action enum defined below:

use enum_iterator::Sequence;

#[derive(Clone, Copy, Default, Sequence)]
enum Size {
    Small,
    #[default]
    Medium,
    Large,
}

#[derive(Clone, Copy, Sequence)]
enum Action {
    Insert,
    Size(Size),
    Delete,
}

What items are expected in the menu? I would expect the following:

• Insert
• Size(Small)
• Size(Medium)
• Size(Large)
• Delete

If I understand this PR correctly, the menu would instead look as follows:

• Insert
• Size(Medium)
• Delete

Why are other sizes ignored? I am trying to understand the rationale for considering only default values of variant fields.