X-Git-Url: https://git.ralfj.de/rust-101.git/blobdiff_plain/63b7a79069a399c32d575bb71832fcad134117c9..c2e9145b487a8bd3d31c5a6f318c86aaf3f9d17d:/src/part12.rs diff --git a/src/part12.rs b/src/part12.rs index 8b04fb6..34e994e 100644 --- a/src/part12.rs +++ b/src/part12.rs @@ -89,7 +89,7 @@ fn demo_cell(c: &mut Callbacks) { //@ is a shared reference. However, it has to increment the reference count! Internally, `Rc` uses `Cell` for the count, such that it //@ can be updated during `clone`. //@ -//@ Putting it all together, the story around mutation and ownership through references looks as follows: There are *exclusive* references, +//@ Putting it all together, the story around mutation and ownership through references looks as follows: There are *unique* references, //@ which - because of their exclusivity - are always safe to mutate through. And there are *shared* references, where the compiler cannot //@ generally promise that mutation is safe. However, if extra circumstances guarantee that mutation *is* safe, then it can happen even //@ through a sahred reference - as we saw with `Cell`. @@ -135,8 +135,8 @@ impl CallbacksMut { //@ the check will always succeed, as is actually entirely useless. However, this is not actually true. Several different `CallbacksMut` could share //@ a callback (as they were created with `clone`), and calling one callback here could trigger calling //@ all callbacks of the other `CallbacksMut`, which would end up calling the initial callback again. This issue of functions accidentally recursively calling - //@ themselves is called *reentrancy*, and it can lead to subtle bugs. Here, it would mean that the closure runs twice, each time thinking it has an - //@ exclusive, mutable reference to its environment - so it may end up dereferencing a dangling pointer. Ouch! Lucky enough, + //@ themselves is called *reentrancy*, and it can lead to subtle bugs. Here, it would mean that the closure runs twice, each time thinking it has a + //@ unique, mutable reference to its environment - so it may end up dereferencing a dangling pointer. Ouch! Lucky enough, //@ Rust detects this at run-time and panics once we try to borrow the same environment again. I hope this also makes it //@ clear that there's absolutely no hope of Rust performing these checks statically, at compile-time: It would have to detect reentrancy! let mut closure = callback.borrow_mut();