feat(corelib): Iterator::last

[MagisterDaIlis]

Keeping this as draft, as I'm getting some issues regarding impl inference:

error: Cannot infer negative impl in `core::option::DestructOption::<Iterator::Item, +Destruct<Self::Item>, _>` as it contains the unresolved type `core::option::Option::<Iterator::Item>`
 --> corelib/src/iter/traits/iterator.cairo:112:15
        Self::fold(ref self, Option::None, some)

[reviewable-StarkWare]

This change is 

[orizi]

Reviewed all commit messages.
Reviewable status: 0 of 2 files reviewed, 1 unresolved discussion (waiting on @MagisterDaIlis)

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corelib/src/test/iter_test.cairo line 19 at r1 (raw file):

    let mut a = ArrayTrait::<u8>::new().into_iter();
    assert_eq!(a.last(), Option::None);

Suggestion:

    assert_eq!(array![1_u8, 2, 3].into_iter().last(), Option::Some(3));
    assert_eq!(array![].into_iter().last().last(), Option::<u8>::None);

[orizi]

Reviewable status: 0 of 2 files reviewed, 2 unresolved discussions (waiting on @MagisterDaIlis)

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corelib/src/iter/traits/iterator.cairo line 110 at r1 (raw file):

        let some = |_acc: Option<Self::Item>, x: Self::Item| {
            Option::Some(x)
        };

to support destruct:

Suggestion:

        let some = |acc: Option<Self::Item>, x: Self::Item| {
            // Hack to use `Destruct<T>` directly, instead of `Destruct<Option<T>>`.
            match acc {
                Some(_) | None => {}
            };
            Option::Some(x)
        };

[orizi]

please respond in https://reviewable.io/reviews/starkware-libs/cairo/7140#-

Reviewed all commit messages.
Reviewable status: 0 of 2 files reviewed, 2 unresolved discussions (waiting on @MagisterDaIlis)

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corelib/src/test/iter_test.cairo line 19 at r1 (raw file):

    let mut a = ArrayTrait::<u8>::new().into_iter();
    assert_eq!(a.last(), Option::None);

Not done yet.

[MagisterDaIlis]

Reviewable status: 0 of 2 files reviewed, 2 unresolved discussions (waiting on @orizi)

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corelib/src/iter/traits/iterator.cairo line 110 at r1 (raw file):

Previously, orizi wrote…

to support destruct:

unfortunately, doesn't help: the error still occurs

error: Cannot infer negative impl in `core::option::DestructOption::<Iterator::Item, +Destruct<Self::Item>, _>` as it contains the unresolved type `core::option::Option::<Iterator::Item>`
 --> corelib/src/iter/traits/iterator.cairo:116:15
        Self::fold(ref self, Option::None, some)

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corelib/src/test/iter_test.cairo line 19 at r1 (raw file):

Previously, orizi wrote…

Not done yet.

second form is not working.

error[E0002]: Method `last` could not be called on type `core::option::Option::<?37>`.
Candidate `core::iter::traits::iterator::Iterator::last` inference failed with: Trait has no implementation in context: core::iter::traits::iterator::Iterator::<core::option::Option::<?37>>.
 --> corelib/src/test/iter_test.cairo:16:44
    assert_eq!(array![].into_iter().last().last(), Option::<u8>::None);

[MagisterDaIlis]

Reviewable status: 0 of 2 files reviewed, 2 unresolved discussions (waiting on @orizi)

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corelib/src/test/iter_test.cairo line 19 at r1 (raw file):

Previously, MagisterDaIlis wrote…

second form is not working.

error[E0002]: Method `last` could not be called on type `core::option::Option::<?37>`.
Candidate `core::iter::traits::iterator::Iterator::last` inference failed with: Trait has no implementation in context: core::iter::traits::iterator::Iterator::<core::option::Option::<?37>>.
 --> corelib/src/test/iter_test.cairo:16:44
    assert_eq!(array![].into_iter().last().last(), Option::<u8>::None);

Done. actually, my bad, last was repeated.

[orizi]

Reviewable status: 0 of 2 files reviewed, 2 unresolved discussions (waiting on @MagisterDaIlis)

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corelib/src/iter/traits/iterator.cairo line 110 at r1 (raw file):

Previously, MagisterDaIlis wrote…

unfortunately, doesn't help: the error still occurs

error: Cannot infer negative impl in `core::option::DestructOption::<Iterator::Item, +Destruct<Self::Item>, _>` as it contains the unresolved type `core::option::Option::<Iterator::Item>`
 --> corelib/src/iter/traits/iterator.cairo:116:15
        Self::fold(ref self, Option::None, some)

is this the entire error? or are you truncating some parts?

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corelib/src/test/iter_test.cairo line 19 at r1 (raw file):

Previously, MagisterDaIlis wrote…

second form is not working.

error[E0002]: Method `last` could not be called on type `core::option::Option::<?37>`.
Candidate `core::iter::traits::iterator::Iterator::last` inference failed with: Trait has no implementation in context: core::iter::traits::iterator::Iterator::<core::option::Option::<?37>>.
 --> corelib/src/test/iter_test.cairo:16:44
    assert_eq!(array![].into_iter().last().last(), Option::<u8>::None);

i called .last() twice in my comment. (and you seem to have copied it)

[MagisterDaIlis]

Reviewable status: 0 of 2 files reviewed, 1 unresolved discussion (waiting on @orizi)

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corelib/src/iter/traits/iterator.cairo line 110 at r1 (raw file):

Previously, orizi wrote…

is this the entire error? or are you truncating some parts?

yes, this is the entire error.

[orizi]

Reviewed all commit messages.
Reviewable status: 0 of 2 files reviewed, 1 unresolved discussion (waiting on @MagisterDaIlis)

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corelib/src/iter/traits/iterator.cairo line 110 at r1 (raw file):

Previously, MagisterDaIlis wrote…

yes, this is the entire error.

oh - it is because Self::fold requires it...
Replied with a suggestion without fold.

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corelib/src/iter/traits/iterator.cairo line 116 at r3 (raw file):

        };

        Self::fold(ref self, Option::None, some)

Suggestion:

        let mut self = self;
        let next = Self::next(ref self)?;
        Option::Some(Self::last(self).unwrap_or(next))

[MagisterDaIlis]

Reviewable status: 0 of 2 files reviewed, 1 unresolved discussion (waiting on @orizi)

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corelib/src/iter/traits/iterator.cairo line 116 at r3 (raw file):

        };

        Self::fold(ref self, Option::None, some)

Done. Very clever!

[orizi]

Reviewed 1 of 1 files at r3, 1 of 1 files at r4, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @MagisterDaIlis)

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a discussion (no related file):
@gilbens-starkware @ilyalesokhin-starkware for 2nd eye.