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Split code example into individual match cases; add code for example

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Philipp Oppermann
2020-02-20 14:40:47 +01:00
parent 7ce491df53
commit 2ff011ffba
1 changed files with 56 additions and 51 deletions
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107
blog/content/second-edition/posts/12-async-await/index.md
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@@ -387,62 +387,67 @@ TODO
```rust
impl Future for ExampleStateMachine {
type Output = String; // return type of `example`
fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
loop {
match self { // TODO: handle pinning
ExampleStateMachine::Start(state) => {
// from body of `example`
let foo_txt_future = async_read_file("foo.txt");
// `.await` operation
let state = WaitingOnFooTxtState {
min_len: state.min_len,
foo_txt_future,
};
*self = ExampleStateMachine::WaitingOnFooTxt(state);
}
ExampleStateMachine::WaitingOnFooTxt(state) => {
match state.foo_txt_future.poll(cx) {
Poll::Pending => return Poll::Pending,
Poll::Ready(content) => {
// from body of `example`
if content.len() < state.min_len {
let bar_txt_future = async_read_file("bar.txt");
// `.await` operation
let state = WaitingOnBarTxtState {
content,
bar_txt_future,
};
*self = ExampleStateMachine::WaitingOnBarTxt(state);
} else {
*self = ExampleStateMachine::End(EndState));
return Poll::Ready(content);
}
}
}
}
ExampleStateMachine::WaitingOnFooTxt(state) => {
match state.bar_txt_future.poll(cx) {
match state.bar_txt_future.poll(cx) {
Poll::Pending => return Poll::Pending,
Poll::Ready(bar_txt) => {
*self = ExampleStateMachine::End(EndState));
// from body of `example`
return Poll::Ready(state.content + &bar_txt);
}
}
}
}
ExampleStateMachine::End(_) => {
panic!("poll called after Poll::Ready was returned");
}
ExampleStateMachine::Start(state) => {
// from body of `example`
let foo_txt_future = async_read_file("foo.txt");
// `.await` operation
let state = WaitingOnFooTxtState {
min_len: state.min_len,
foo_txt_future,
};
*self = ExampleStateMachine::WaitingOnFooTxt(state);
}
```
```rust
ExampleStateMachine::WaitingOnFooTxt(state) => {
match state.foo_txt_future.poll(cx) {
Poll::Pending => return Poll::Pending,
Poll::Ready(content) => {
// from body of `example`
if content.len() < state.min_len {
let bar_txt_future = async_read_file("bar.txt");
// `.await` operation
let state = WaitingOnBarTxtState {
content,
bar_txt_future,
};
*self = ExampleStateMachine::WaitingOnBarTxt(state);
} else {
*self = ExampleStateMachine::End(EndState));
return Poll::Ready(content);
}
}
}
}
```
```rust
ExampleStateMachine::WaitingOnFooTxt(state) => {
match state.bar_txt_future.poll(cx) {
match state.bar_txt_future.poll(cx) {
Poll::Pending => return Poll::Pending,
Poll::Ready(bar_txt) => {
*self = ExampleStateMachine::End(EndState));
// from body of `example`
return Poll::Ready(state.content + &bar_txt);
}
}
}
}
```
```rust
ExampleStateMachine::End(_) => {
panic!("poll called after Poll::Ready was returned");
}
```
```rust
fn example(min_len: usize) -> ExampleStateMachine {
ExampleStateMachine::Start(StartState {
min_len,
})
}
```
### Pinning