syntax sugar

• for-loop syntax - is actually syntax sugar for iterators
• impl Trait syntax - is actually syntax sugar for a trait bound

impl Trait syntax

The impl Trait syntax works for straightforward cases but is actually syntax sugar for a longer form known as a trait bound.

// the following are the same

// case 1: syntax sugar
pub fn notify(item: &impl Summary) {
    println!("Breaking news! {}", item.summarize());
}

// case 2: trait bound
pub fn notify<T: Summary>(item: &T) {
    println!("Breaking news! {}", item.summarize());
}