What is the difference between iter and into_iter in Rust?

In Rust, iter and into_iter are methods used to create iterators from collections, but they differ significantly in how they handle ownership and mutability.

iter()

• Purpose: Creates an iterator that borrows each element of the collection immutably.
• Ownership: The original collection is not consumed, meaning it remains available for use after the iteration.
• Usage: Suitable when you need to read elements without modifying the collection.
• Example:

  let vec = vec![1, 2, 3];
  let mut iter = vec.iter();
  assert_eq!(iter.next(), Some(&1));
  assert_eq!(iter.next(), Some(&2));
  assert_eq!(iter.next(), Some(&3));
  assert_eq!(iter.next(), None);
  // vec is still usable here

into_iter()

• Purpose: Creates an iterator that takes ownership of the collection, consuming it.
• Ownership: The original collection is consumed, meaning it cannot be used after the iteration.
• Usage: Suitable when you need to take ownership of the elements, often for transforming or moving them.
• Example:

  let vec = vec![1, 2, 3];
  let mut iter = vec.into_iter();
  assert_eq!(iter.next(), Some(1));
  assert_eq!(iter.next(), Some(2));
  assert_eq!(iter.next(), Some(3));
  assert_eq!(iter.next(), None);
  // vec is no longer usable here

Key Differences

1. Ownership Transfer:

   • iter(): Borrows elements immutably, does not consume the collection.
   • into_iter(): Takes ownership of elements, consumes the collection.

2. Mutability:

   • iter(): Provides immutable references to the elements.
   • into_iter(): Provides owned values, allowing for transformations that require ownership.

3. Post-Iteration Use:

   • iter(): The original collection remains usable after iteration.
   • into_iter(): The original collection is no longer usable after iteration.

Practical Implications

• Use iter() when you ne...