How to iterate prefixes or suffixes of vec or slice in rust?

Question

I have a vec: vec![1, 2, 3, 4]. I want to know how to:

• Iterate its prefixes from shortest to longest:

  &[], &[1], &[1, 2], &[1, 2, 3], &[1, 2, 3, 4]

• Iterate its prefixes from longest to shortest:

  &[1, 2, 3, 4], &[1, 2, 3], &[1, 2], &[1], &[]

• Iterate its suffixes from shortest to longest:

  &[], &[4], &[3, 4], &[2, 3, 4], &[1, 2, 3, 4]

• Iterate its suffixes from longest to shortest:

  &[1, 2, 3, 4], &[2, 3, 4], &[3, 4], &[4], &[],

Answer 1

See also: How to iterate prefixes and suffixes of str or String in rust?

• What works for a &[T] (i.e. a slice) will also work for &Vec<T> due to Deref coercion

• To construct a range of indexes from 0 to slice.len() inclusive: 0..=slice.len()

• std::ops::Range implements both Iterator and DoubleEndedIterator. This allows you to use the rev() method:

  (0..=slice.len()).rev()

• To get a prefix of a given length: &slice[..len]

• To get a suffix without the first cut items: &slice[cut..]

Putting it all together

To iterate from shortest to longest:

pub fn prefixes_asc<T>(slice: &[T]) -> impl Iterator<Item = &[T]> + DoubleEndedIterator {
    (0..=slice.len()).map(move |len| &slice[..len])
}

pub fn suffixes_asc<T>(slice: &[T]) -> impl Iterator<Item = &[T]> + DoubleEndedIterator {
    (0..=slice.len()).rev().map(move |cut| &slice[cut..])
}

To reverse just use .rev():

pub fn prefixes_desc<T>(slice: &[T]) -> impl Iterator<Item = &[T]> + DoubleEndedIterator {
    prefixes_asc(slice).rev()
}

pub fn suffixes_desc<T>(slice: &[T]) -> impl Iterator<Item = &[T]> + DoubleEndedIterator {
    suffixes_asc(slice).rev()
}

tests