Rust: What is the difference between async fn and fn returning Future?

async fn — syntactic sugar. fn -> Future — explicit.

async fn:

• Cleaner syntax.
• Compiler generates Future.
• Cannot return different Future types.

fn -> Future:

• Explicit Future return.
• Can return different types.
• More flexible.

1// Async fn
2async fn get_data() -> String {
3    String::from("data")
4}
5
6// Fn returning Future
7fn get_data() -> impl Future<Output = String> {
8    async { String::from("data") }
9}

Key: async fn for simple cases, explicit Future for flexibility.