There are a large number of places that incorrectly refer
to deriving in comments, instead of derives.
If someone could look at src/etc/generate-deriving-span-tests.py,
I'm not sure how those tests were passing before/if they were.
Currently, we build a closure that does nothing but pass its argument
through to another function, this is rather wasteful and creates lots of
unnecessary closures.
Currently, we build a closure that does nothing but pass its argument
through to another function, this is rather wasteful and creates lots of
unnecessary closures.
This commit performs a pass over the `std::macros` module, applying stability
attributes where necessary. In particular, this audits macros for patterns such
as:
* Standard use of forward-to-format-args via `$($arg:tt)*` (or `+`)
* Prevent macro-defined identifiers from leaking into expression arguments as
hygiene is not perfectly implemented.
* Wherever possible, `$crate` is used now.
Specifically, the following actions were taken:
* The `std::macros` module itself is no longer public.
* The `panic!` macro is stable
* The `assert!` macro is stable
* The `assert_eq!` macro is stable
* The `debug_assert!` macro is stable
* The `debug_assert_eq!` macro is stable
* The `unreachable!` macro is stable after removing the extra forms to bring the
definition in line with the `unimplemented!` macro.
* The `try!` macro is stable
* The `vec!` macro is stable
[breaking-change]
This commit aims to prepare the `std::hash` module for alpha by formalizing its
current interface whileholding off on adding `#[stable]` to the new APIs. The
current usage with the `HashMap` and `HashSet` types is also reconciled by
separating out composable parts of the design. The primary goal of this slight
redesign is to separate the concepts of a hasher's state from a hashing
algorithm itself.
The primary change of this commit is to separate the `Hasher` trait into a
`Hasher` and a `HashState` trait. Conceptually the old `Hasher` trait was
actually just a factory for various states, but hashing had very little control
over how these states were used. Additionally the old `Hasher` trait was
actually fairly unrelated to hashing.
This commit redesigns the existing `Hasher` trait to match what the notion of a
`Hasher` normally implies with the following definition:
trait Hasher {
type Output;
fn reset(&mut self);
fn finish(&self) -> Output;
}
This `Hasher` trait emphasizes that hashing algorithms may produce outputs other
than a `u64`, so the output type is made generic. Other than that, however, very
little is assumed about a particular hasher. It is left up to implementors to
provide specific methods or trait implementations to feed data into a hasher.
The corresponding `Hash` trait becomes:
trait Hash<H: Hasher> {
fn hash(&self, &mut H);
}
The old default of `SipState` was removed from this trait as it's not something
that we're willing to stabilize until the end of time, but the type parameter is
always required to implement `Hasher`. Note that the type parameter `H` remains
on the trait to enable multidispatch for specialization of hashing for
particular hashers.
Note that `Writer` is not mentioned in either of `Hash` or `Hasher`, it is
simply used as part `derive` and the implementations for all primitive types.
With these definitions, the old `Hasher` trait is realized as a new `HashState`
trait in the `collections::hash_state` module as an unstable addition for
now. The current definition looks like:
trait HashState {
type Hasher: Hasher;
fn hasher(&self) -> Hasher;
}
The purpose of this trait is to emphasize that the one piece of functionality
for implementors is that new instances of `Hasher` can be created. This
conceptually represents the two keys from which more instances of a
`SipHasher` can be created, and a `HashState` is what's stored in a
`HashMap`, not a `Hasher`.
Implementors of custom hash algorithms should implement the `Hasher` trait, and
only hash algorithms intended for use in hash maps need to implement or worry
about the `HashState` trait.
The entire module and `HashState` infrastructure remains `#[unstable]` due to it
being recently redesigned, but some other stability decision made for the
`std::hash` module are:
* The `Writer` trait remains `#[experimental]` as it's intended to be replaced
with an `io::Writer` (more details soon).
* The top-level `hash` function is `#[unstable]` as it is intended to be generic
over the hashing algorithm instead of hardwired to `SipHasher`
* The inner `sip` module is now private as its one export, `SipHasher` is
reexported in the `hash` module.
And finally, a few changes were made to the default parameters on `HashMap`.
* The `RandomSipHasher` default type parameter was renamed to `RandomState`.
This renaming emphasizes that it is not a hasher, but rather just state to
generate hashers. It also moves away from the name "sip" as it may not always
be implemented as `SipHasher`. This type lives in the
`std::collections::hash_map` module as `#[unstable]`
* The associated `Hasher` type of `RandomState` is creatively called...
`Hasher`! This concrete structure lives next to `RandomState` as an
implemenation of the "default hashing algorithm" used for a `HashMap`. Under
the hood this is currently implemented as `SipHasher`, but it draws an
explicit interface for now and allows us to modify the implementation over
time if necessary.
There are many breaking changes outlined above, and as a result this commit is
a:
[breaking-change]
There's been some debate over the precise form that these APIs should take, and
they've undergone some changes recently, so these APIs are going to be left
unstable for now to be fleshed out during the next release cycle.
fmt::Show is for debugging, and can and should be implemented for
all public types. This trait is used with `{:?}` syntax. There still
exists #[derive(Show)].
fmt::String is for types that faithfully be represented as a String.
Because of this, there is no way to derive fmt::String, all
implementations must be purposeful. It is used by the default format
syntax, `{}`.
This will break most instances of `{}`, since that now requires the type
to impl fmt::String. In most cases, replacing `{}` with `{:?}` is the
correct fix. Types that were being printed specifically for users should
receive a fmt::String implementation to fix this.
Part of #20013
[breaking-change]
See RFC 550 (https://github.com/rust-lang/rfcs/pull/550) for the motivation
and details.
If this breaks your code, add one of the listed tokens after the relevant
non-terminal in your matcher.
[breaking-change]
These aren't in their final form, but are all aiming to be part of 1.0, so at the very least encouraging usage now to find the bugs is nice.
Also, the widespread roll-out of associated types in the standard library indicates they're getting good, and it's lame to have to activate a feature in essentially every crate ever.
macro_rules! is like an item that defines a macro. Other items don't have a
trailing semicolon, or use a paren-delimited body.
If there's an argument for matching the invocation syntax, e.g. parentheses for
an expr macro, then I think that applies more strongly to the *inner*
delimiters on the LHS, wrapping the individual argument patterns.
