Turning a `&T` into an `&mut T` carries a large risk of undefined
behaviour, and needs to be done very very carefully. Providing a
convenience function for exactly this task is a bad idea, just tempting
people into doing the wrong thing.
The right thing is to use types like `Cell`, `RefCell` or `Unsafe`.
For memory safety, Rust has that guarantee that `&mut` pointers do not
alias with any other pointer, that is, if you have a `&mut T` then that
is the only usable pointer to that `T`. This allows Rust to assume that
writes through a `&mut T` do not affect the values of any other `&` or
`&mut` references. `&` pointers have no guarantees about aliasing or
not, so it's entirely possible for the same pointer to be passed into
both arguments of a function like
fn foo(x: &int, y: &int) { ... }
Converting either of `x` or `y` to a `&mut` pointer and modifying it
would affect the other value: invalid behaviour.
(Similarly, it's undefined behaviour to modify the value of an immutable
local, like `let x = 1;`.)
At a low-level, the *only* safe way to obtain an `&mut` out of a `&` is
using the `Unsafe` type (there are higher level wrappers around it, like
`Cell`, `RefCell`, `Mutex` etc.). The `Unsafe` type is registered with
the compiler so that it can reason a little about these `&` to `&mut`
casts, but it is still up to the user to ensure that the `&mut`s
obtained out of an `Unsafe` never alias.
(Note that *any* conversion from `&` to `&mut` can be invalid, including
a plain `transmute`, or casting `&T` -> `*T` -> `*mut T` -> `&mut T`.)
[breaking-change]
Most of the links I've removed are for types that don't exist anymore with the exception of `SendReceiver` though I'm not sure how useful it is to link to that without the accompanying `Receiver` and `Sender` and I don't know how useful those links are when they're discussed below and `channel`/`sync_channel` is on the `std::comm` page already linked.
If an unbalanced [ exists in a string or comment, this should not be
considered when calculating the indent at the top level.
Similarly, when testing for ({/}) to see if we're at the top level to
begin with, strings and comments should be skipped.
Previously, windows was using the CREATE_NEW flag which fails if the file
previously existed, which differed from the unix semantics. This alters the
opening to use the OPEN_ALWAYS flag to mirror the unix semantics.
Closes#13861
This has long since not been too relevant since the introduction of many crate
type outputs. This commit removes the flag entirely, adjusting all logic to do
the most reasonable thing when building both a library and an executable.
Closes#13337
Improve tutorial discussion of closures, e.g. with respect to type inference and variable capture.
Fix#13621
---- original description follows
I'd like this pulled to master if possible but if not I'd appreciate comments on what I need to change. I found the closures difficult to understand as they were so I tried to explain it so I would've had an easier time understanding it. I think it's better at least, somewhat.
I don't know that everyone liked the `-> ()` I included but I thought explicit is best to aid understanding. I thought it was much harder to understand than it should have been.
[EDIT] - Clicked too early.
This doesn't `make check` without errors on my Xubuntu on Virtualbox machine. Not sure why. I don't think I changed anything problematic. I'll try `make check` on master tomorrow.
Opened https://github.com/mozilla/rust/issues/13621 regarding this.
- using libgreen to optimize CPU usage
- less tasks to limit wasted resources
Here, on a one core 2 threads CPU, new version is ~1.2 faster. May
be better with more core.
This was removed because these could alias with `&const T` or `@mut T`
and those are now gone from the language. There are still aliasing
issues within local scopes, but this is correct for function parameters.
This also removes the no-op `noalias` marker on proc (not a pointer) and
leaves out the mention of #6750 because real type-based alias analysis
is not within the scope of best effort usage of the `noalias` attribute.
Test case:
pub fn foo(x: &mut &mut u32) {
**x = 5;
**x = 5;
}
Before:
define void @_ZN3foo20h0ce94c9671b0150bdaa4v0.0E(i32** nocapture readonly) unnamed_addr #0 {
entry-block:
%1 = load i32** %0, align 8
store i32 5, i32* %1, align 4
%2 = load i32** %0, align 8
store i32 5, i32* %2, align 4
ret void
}
After:
define void @_ZN3foo20h0ce94c9671b0150bdaa4v0.0E(i32** noalias nocapture readonly) unnamed_addr #0 {
entry-block:
%1 = load i32** %0, align 8
store i32 5, i32* %1, align 4
ret void
}
Closes#12436
The years of copyright and the name of the copyright holder were not
present in the notice.
The Apache license was added to the project in 2012, so 2012 is the
starting year. The copyright holder is the Mozilla Foundation (taken
from the MIT license).
This commit removes the inherited documentation from type pages. This generally
just clutters up the page when you can click through to the trait itself to get
all the meaty documentation.
Closes#11991
This primary fix brought on by this upgrade is the proper matching of the ```
and ~~~ doc blocks. This also moves hoedown to a git submodule rather than a
bundled repository.
Additionally, hoedown is stricter about code blocks, so this ended up fixing a
lot of invalid code blocks (ending with " ```" instead of "```", or ending with
"~~~~" instead of "~~~").
Closes#12776
This ensures that private functions exported through static initializers will
actually end up being public in the object file (so other objects can continue
to reference the function).
Closes#13620
- using libgreen to optimize CPU usage
- less tasks to limit wasted resources
Here, on a one core 2 threads CPU, new version is ~1.2 faster. May
be better with more core.
Closes#7575.
I don't think the change from a contains lookup to an iteration of the HashSet in the resolver should be much of a burden as the set of methods with the same name should be relatively small.
This is a first patch towards an opt-in built-in trait world. This patch removes the restriction on built-in traits and allows such traits to be derived.
[RFC#3]
cc #13231
@nikomatsakis r?
This allows writing code examples which pass all analysis of the compiler, but
don't actually link. A good example is examples that use extern {} blocks.
Closes#12903
Rustdoc currently doesn't inline documentation of a `pub use` if the target is
publicly reachable. This changes rustdoc to allow a #[doc(inline)] attribute to
force inlining the documentation, regardless of whether the targe is public or
not.
Closes#13045
The outer attributes were manually appended when a module file was parsed, but
the attributes were also added higher up the stack of parsing (when the module
finished parsing). This removes the append in parsing the module file.
Closes#13826
