Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Add move_ref_pattern docs #881

Merged
merged 1 commit into from
Oct 17, 2020
Merged

Add move_ref_pattern docs #881

merged 1 commit into from
Oct 17, 2020

Conversation

Amjad50
Copy link
Contributor

@Amjad50 Amjad50 commented Aug 29, 2020 •
edited
Loading

Documenting move_ref_pattern for stabilization. (see rust-lang/rust#76049)

This is waiting for the stabilizing PR to be merged

This was referenced Aug 29, 2020
Closed
Closed
Merged
@ehuss ehuss added the S-waiting-on-stabilization Waiting for a stabilization PR to be merged in the main Rust repository label Aug 31, 2020
JohnTitor added a commit to JohnTitor/rust that referenced this pull request Oct 15, 2020
@JohnTitor
Rollup merge of rust-lang#76119 - Amjad50:stabilizing-move_ref_patter…
c8ca030 
…n, r=nikomatsakis

Stabilize move_ref_pattern

# Implementation
- Initially the rule was added in the run-up to 1.0. The AST-based borrow checker was having difficulty correctly enforcing match expressions that combined ref and move bindings, and so it was decided to simplify forbid the combination out right.
- The move to MIR-based borrow checking made it possible to enforce the rules in a finer-grained level, but we kept the rule in place in an effort to be conservative in our changes.
- In rust-lang#68376, @Centril lifted the restriction but required a feature-gate.
- This PR removes the feature-gate.

Tracking issue: rust-lang#68354.

# Description
This PR is to stabilize the feature `move_ref_pattern`, which allows patterns
containing both `by-ref` and `by-move` bindings at the same time.

For example: `Foo(ref x, y)`, where `x` is `by-ref`,
and `y` is `by-move`.

The rules of moving a variable also apply here when moving *part* of a variable,
such as it can't be referenced or moved before.

If this pattern is used, it would result in *partial move*, which means that
part of the variable is moved. The variable that was partially moved from
cannot be used as a whole in this case, only the parts that are still
not moved can be used.

## Documentation
- The reference (rust-lang/reference#881)
- Rust by example (rust-lang/rust-by-example#1377)

## Tests
There are many tests, but I think one of the comperhensive ones:
- [borrowck-move-ref-pattern-pass.rs](https://github.com/Centril/rust/blob/85fbf49ce0e2274d0acf798f6e703747674feec3/src/test/ui/pattern/move-ref-patterns/borrowck-move-ref-pattern-pass.rs)
- [borrowck-move-ref-pattern.rs](https://github.com/Centril/rust/blob/85fbf49ce0e2274d0acf798f6e703747674feec3/src/test/ui/pattern/move-ref-patterns/borrowck-move-ref-pattern.rs)

# Examples

```rust
#[derive(PartialEq, Eq)]
struct Finished {}

#[derive(PartialEq, Eq)]
struct Processing {
    status: ProcessStatus,
}

#[derive(PartialEq, Eq)]
enum ProcessStatus {
    One,
    Two,
    Three,
}

#[derive(PartialEq, Eq)]
enum Status {
    Finished(Finished),
    Processing(Processing),
}

fn check_result(_url: &str) -> Status {
    // fetch status from some server
    Status::Processing(Processing {
        status: ProcessStatus::One,
    })
}

fn wait_for_result(url: &str) -> Finished {
    let mut previous_status = None;
    loop {
        match check_result(url) {
            Status::Finished(f) => return f,
            Status::Processing(p) => {
                match (&mut previous_status, p.status) {
                    (None, status) => previous_status = Some(status), // first status
                    (Some(previous), status) if *previous == status => {} // no change, ignore
                    (Some(previous), status) => { // Now it can be used
                        // new status
                        *previous = status;
                    }
                }
            }
        }
    }
}
```

Before, we would have used:
```rust
                match (&previous_status, p.status) {
                    (Some(previous), status) if *previous == status => {} // no change, ignore
                    (_, status) => {
                        // new status
                        previous_status = Some(status);
                    }
                }
```

Demonstrating *partial move*
```rust
fn main() {
    #[derive(Debug)]
    struct Person {
        name: String,
        age: u8,
    }

    let person = Person {
        name: String::from("Alice"),
        age: 20,
    };

    // `name` is moved out of person, but `age` is referenced
    let Person { name, ref age } = person;

    println!("The person's age is {}", age);

    println!("The person's name is {}", name);

    // Error! borrow of partially moved value: `person` partial move occurs
    //println!("The person struct is {:?}", person);

    // `person` cannot be used but `person.age` can be used as it is not moved
    println!("The person's age from person struct is {}", person.age);
}
```
Dylan-DPC-zz pushed a commit to Dylan-DPC-zz/rust that referenced this pull request Oct 15, 2020
@Dylan-DPC
Rollup merge of rust-lang#76119 - Amjad50:stabilizing-move_ref_patter…
2c74117 
…n, r=nikomatsakis

Stabilize move_ref_pattern

# Implementation
- Initially the rule was added in the run-up to 1.0. The AST-based borrow checker was having difficulty correctly enforcing match expressions that combined ref and move bindings, and so it was decided to simplify forbid the combination out right.
- The move to MIR-based borrow checking made it possible to enforce the rules in a finer-grained level, but we kept the rule in place in an effort to be conservative in our changes.
- In rust-lang#68376, @Centril lifted the restriction but required a feature-gate.
- This PR removes the feature-gate.

Tracking issue: rust-lang#68354.

# Description
This PR is to stabilize the feature `move_ref_pattern`, which allows patterns
containing both `by-ref` and `by-move` bindings at the same time.

For example: `Foo(ref x, y)`, where `x` is `by-ref`,
and `y` is `by-move`.

The rules of moving a variable also apply here when moving *part* of a variable,
such as it can't be referenced or moved before.

If this pattern is used, it would result in *partial move*, which means that
part of the variable is moved. The variable that was partially moved from
cannot be used as a whole in this case, only the parts that are still
not moved can be used.

## Documentation
- The reference (rust-lang/reference#881)
- Rust by example (rust-lang/rust-by-example#1377)

## Tests
There are many tests, but I think one of the comperhensive ones:
- [borrowck-move-ref-pattern-pass.rs](https://github.com/Centril/rust/blob/85fbf49ce0e2274d0acf798f6e703747674feec3/src/test/ui/pattern/move-ref-patterns/borrowck-move-ref-pattern-pass.rs)
- [borrowck-move-ref-pattern.rs](https://github.com/Centril/rust/blob/85fbf49ce0e2274d0acf798f6e703747674feec3/src/test/ui/pattern/move-ref-patterns/borrowck-move-ref-pattern.rs)

# Examples

```rust
#[derive(PartialEq, Eq)]
struct Finished {}

#[derive(PartialEq, Eq)]
struct Processing {
    status: ProcessStatus,
}

#[derive(PartialEq, Eq)]
enum ProcessStatus {
    One,
    Two,
    Three,
}

#[derive(PartialEq, Eq)]
enum Status {
    Finished(Finished),
    Processing(Processing),
}

fn check_result(_url: &str) -> Status {
    // fetch status from some server
    Status::Processing(Processing {
        status: ProcessStatus::One,
    })
}

fn wait_for_result(url: &str) -> Finished {
    let mut previous_status = None;
    loop {
        match check_result(url) {
            Status::Finished(f) => return f,
            Status::Processing(p) => {
                match (&mut previous_status, p.status) {
                    (None, status) => previous_status = Some(status), // first status
                    (Some(previous), status) if *previous == status => {} // no change, ignore
                    (Some(previous), status) => { // Now it can be used
                        // new status
                        *previous = status;
                    }
                }
            }
        }
    }
}
```

Before, we would have used:
```rust
                match (&previous_status, p.status) {
                    (Some(previous), status) if *previous == status => {} // no change, ignore
                    (_, status) => {
                        // new status
                        previous_status = Some(status);
                    }
                }
```

Demonstrating *partial move*
```rust
fn main() {
    #[derive(Debug)]
    struct Person {
        name: String,
        age: u8,
    }

    let person = Person {
        name: String::from("Alice"),
        age: 20,
    };

    // `name` is moved out of person, but `age` is referenced
    let Person { name, ref age } = person;

    println!("The person's age is {}", age);

    println!("The person's name is {}", name);

    // Error! borrow of partially moved value: `person` partial move occurs
    //println!("The person struct is {:?}", person);

    // `person` cannot be used but `person.age` can be used as it is not moved
    println!("The person's age from person struct is {}", person.age);
}
```
Dylan-DPC-zz pushed a commit to Dylan-DPC-zz/rust that referenced this pull request Oct 16, 2020
@Dylan-DPC
Rollup merge of rust-lang#76119 - Amjad50:stabilizing-move_ref_patter…
85dbb03 
…n, r=nikomatsakis

Stabilize move_ref_pattern

# Implementation
- Initially the rule was added in the run-up to 1.0. The AST-based borrow checker was having difficulty correctly enforcing match expressions that combined ref and move bindings, and so it was decided to simplify forbid the combination out right.
- The move to MIR-based borrow checking made it possible to enforce the rules in a finer-grained level, but we kept the rule in place in an effort to be conservative in our changes.
- In rust-lang#68376, @Centril lifted the restriction but required a feature-gate.
- This PR removes the feature-gate.

Tracking issue: rust-lang#68354.

# Description
This PR is to stabilize the feature `move_ref_pattern`, which allows patterns
containing both `by-ref` and `by-move` bindings at the same time.

For example: `Foo(ref x, y)`, where `x` is `by-ref`,
and `y` is `by-move`.

The rules of moving a variable also apply here when moving *part* of a variable,
such as it can't be referenced or moved before.

If this pattern is used, it would result in *partial move*, which means that
part of the variable is moved. The variable that was partially moved from
cannot be used as a whole in this case, only the parts that are still
not moved can be used.

## Documentation
- The reference (rust-lang/reference#881)
- Rust by example (rust-lang/rust-by-example#1377)

## Tests
There are many tests, but I think one of the comperhensive ones:
- [borrowck-move-ref-pattern-pass.rs](https://github.com/Centril/rust/blob/85fbf49ce0e2274d0acf798f6e703747674feec3/src/test/ui/pattern/move-ref-patterns/borrowck-move-ref-pattern-pass.rs)
- [borrowck-move-ref-pattern.rs](https://github.com/Centril/rust/blob/85fbf49ce0e2274d0acf798f6e703747674feec3/src/test/ui/pattern/move-ref-patterns/borrowck-move-ref-pattern.rs)

# Examples

```rust
#[derive(PartialEq, Eq)]
struct Finished {}

#[derive(PartialEq, Eq)]
struct Processing {
    status: ProcessStatus,
}

#[derive(PartialEq, Eq)]
enum ProcessStatus {
    One,
    Two,
    Three,
}

#[derive(PartialEq, Eq)]
enum Status {
    Finished(Finished),
    Processing(Processing),
}

fn check_result(_url: &str) -> Status {
    // fetch status from some server
    Status::Processing(Processing {
        status: ProcessStatus::One,
    })
}

fn wait_for_result(url: &str) -> Finished {
    let mut previous_status = None;
    loop {
        match check_result(url) {
            Status::Finished(f) => return f,
            Status::Processing(p) => {
                match (&mut previous_status, p.status) {
                    (None, status) => previous_status = Some(status), // first status
                    (Some(previous), status) if *previous == status => {} // no change, ignore
                    (Some(previous), status) => { // Now it can be used
                        // new status
                        *previous = status;
                    }
                }
            }
        }
    }
}
```

Before, we would have used:
```rust
                match (&previous_status, p.status) {
                    (Some(previous), status) if *previous == status => {} // no change, ignore
                    (_, status) => {
                        // new status
                        previous_status = Some(status);
                    }
                }
```

Demonstrating *partial move*
```rust
fn main() {
    #[derive(Debug)]
    struct Person {
        name: String,
        age: u8,
    }

    let person = Person {
        name: String::from("Alice"),
        age: 20,
    };

    // `name` is moved out of person, but `age` is referenced
    let Person { name, ref age } = person;

    println!("The person's age is {}", age);

    println!("The person's name is {}", name);

    // Error! borrow of partially moved value: `person` partial move occurs
    //println!("The person struct is {:?}", person);

    // `person` cannot be used but `person.age` can be used as it is not moved
    println!("The person's age from person struct is {}", person.age);
}
```
@ehuss
Copy link
Contributor

ehuss commented Oct 17, 2020

@Amjad50 Now that rust-lang/rust#76119 has merged, is this ready to go?

@Amjad50
Copy link
Contributor Author

Amjad50 commented Oct 17, 2020

The stabilization is not yet into nightly. mdbook test still fail. I guess we need more time.

@Amjad50
Copy link
Contributor Author

Amjad50 commented Oct 17, 2020 •
edited
Loading

No, nvm. nightly 1.49 is already out. Yup this is ready for merge. Can you review it @ehuss ?

@ehuss ehuss removed the S-waiting-on-stabilization Waiting for a stabilization PR to be merged in the main Rust repository label Oct 17, 2020
ehuss
ehuss approved these changes Oct 17, 2020
View reviewed changes
Copy link
Contributor

@ehuss ehuss left a comment

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Great, thanks!

@ehuss ehuss merged commit e526381 into rust-lang:master Oct 17, 2020
@ehuss ehuss mentioned this pull request Oct 28, 2020
Merged
JohnTitor added a commit to JohnTitor/rust that referenced this pull request Oct 29, 2020
@JohnTitor
Rollup merge of rust-lang#78492 - ehuss:update-books, r=ehuss
218af6f 
Update books

## nomicon

7 commits in 6e57e64501f61873ab80cb78a07180a22751a5d6..69333eddb1de92fd17e272ce4677cc983d3bd71d
2020-09-14 11:40:23 -0400 to 2020-10-17 15:44:12 -0700
- Tweak GHA config (rust-lang/nomicon#240)
- Fix link for `[T]` (rust-lang/nomicon#239)
- Update casts.md (rust-lang/nomicon#232)
- [WIP] Add more links (rust-lang/nomicon#180)
- Data Race definition should be more precise (rust-lang/nomicon#219)
- Update the diagnostic of `error[E0597]` in dropck.md (rust-lang/nomicon#157)
- fix typo in Lifetimes mutable reference aliasing section (rust-lang/nomicon#225)

## reference

3 commits in 1b78182e71709169dc0f1c3acdc4541b6860e1c4..10c16caebe475d0d11bec0531b95d7697856c13c
2020-10-11 13:53:47 -0700 to 2020-10-25 20:51:26 -0700
- Add `unsafe` for `mod` and `extern`. (rust-lang/reference#898)
- mention how unions interact with dropping (rust-lang/reference#897)
- Add `move_ref_pattern` docs (rust-lang/reference#881)

## book

2 commits in 451a1e30f2dd137aa04e142414eafb8d05f87f84..13e1c05420bca86ecc79e4ba5b6d02de9bd53c62
2020-10-05 09:11:18 -0500 to 2020-10-20 14:57:32 -0500
- Referencing to Appendix B (rust-lang/book#2481)
- Use GITHUB_PATH instead of add-path (rust-lang/book#2477)

## rust-by-example

2 commits in 152475937a8d8a1f508d8eeb57db79139bc803d9..99eafee0cb14e6ec641bf02a69d7b30f6058349a
2020-10-09 09:29:50 -0300 to 2020-10-21 14:21:55 -0300
- Formatting footer items. (rust-lang/rust-by-example#1385)
- Add partial moves example for `move_ref_pattern` stabilization (rust-lang/rust-by-example#1377)

## edition-guide

3 commits in 81f16863014de60b53de401d71ff904d163ee030..7bc9b7a5e800f79df62947cb7d566fd2fbaf19fe
2020-08-27 13:56:31 -0700 to 2020-10-23 18:31:23 -0500
- A few small updates. (rust-lang/edition-guide#221)
- Clarify the limitation of ? in main and tests (rust-lang/edition-guide#219)
- Update deprecated GitHub Actions commands. (rust-lang/edition-guide#220)
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Reviewers

@ehuss ehuss ehuss approved these changes

Assignees
No one assigned
Labels
None yet
Projects
None yet
Milestone
No milestone
Development

Successfully merging this pull request may close these issues.

None yet
2 participants
@Amjad50 @ehuss