Rust: What is the difference between IntoIterator and Iterator?

IntoIterator — can be iterated. Iterator — provides iteration.

IntoIterator:

• Converts to iterator.
• Consumes self.
• For for loops.

Iterator:

• Provides next.
• Lazy evaluation.
• Composable.

1let v = vec![1, 2, 3];
2
3// IntoIterator: for loop uses this
4for item in v {
5    println!("{}", item);
6}
7
8// Iterator: provides next
9let mut iter = v.into_iter();
10while let Some(item) = iter.next() {
11    println!("{}", item);
12}

Key: IntoIterator for conversion, Iterator for iteration.