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.
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.
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 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 change allow a speedup of ~1.5 on shootout-pidigits on a i32
system. `MachineUint` is used to abstract the internal machine
unsigned integer to simplity future architecture specialization.
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
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
Commits for details.
This shouldn't change the generated code at all (except for switching to `LitBinary` from an explicit ExprVec of individual ExprLit bytes for `prefix_bytes`).
char literals now work in a quotation.
There were several instances of duplicated functionality in regex_macros
compared to AstBuilder so refactor those out.
