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#### Note: this error code is no longer emitted by the compiler.
Sub-bindings, e.g. `ref x @ Some(ref y)` are now allowed under
`#![feature(bindings_after_at)]` and checked to make sure that
memory safety is upheld.
--------------
In certain cases it is possible for sub-bindings to violate memory safety.
Updates to the borrow checker in a future version of Rust may remove this
restriction, but for now patterns must be rewritten without sub-bindings.
Before:
```compile_fail
match Some("hi".to_string()) {
ref op_string_ref @ Some(s) => {},
None => {},
}
```
After:
```
match Some("hi".to_string()) {
Some(ref s) => {
let op_string_ref = &Some(s);
// ...
},
None => {},
}
```
The `op_string_ref` binding has type `&Option<&String>` in both cases.
See also [Issue 14587][issue-14587].
[issue-14587]: https://github.com/rust-lang/rust/issues/14587
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