Sharing

⚠️ DADA DOESN'T REALLY EXIST. ⚠️ See the main tutorial page for more information. Also, you have to pretend that all the code examples are editable and runnable, with live IDE tooltips and so forth. =)

Covers:

• The shared ownership mode and its implications.

Starting point

As our starting point, we'll use the format string example from the basics chapter:

async fn main() {
    var name = “world”
    var greeting = “Hello, {name}”
    print(greeting).await
}

Helper function: greet

Let's introduce a helper function called greet. The role of greet is to compose the greeting and print it to the screen:

async fn main() {
    var name = “world”
    greet(name).await
}

async fn greet(name: String) {
    var greeting = “Hello, {name}”
    print(greeting).await
}

Two important things to note:

• greet is an async function. This is because it is calling print, which is an async function. Try removing the async keyword and see what happens. (Answer: compilation error.)
• Because greet is an async function, calling it yields a thunk which we must await. Try removing the await and running the example and see what happens! (Answer: nothing.)

Why no ownership mode?

You may have noticed that name doesn't have any ownership mode! That's because the only thing we are doing is reading from name. When you write no ownership mode on a function parameter, that means the function can be called with any ownership mode that the caller wants¹.

Sharing mode