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Diffstat (limited to 'library/core/src/ops/function.rs')
-rw-r--r-- | library/core/src/ops/function.rs | 304 |
1 files changed, 304 insertions, 0 deletions
diff --git a/library/core/src/ops/function.rs b/library/core/src/ops/function.rs new file mode 100644 index 000000000..c5a194b7d --- /dev/null +++ b/library/core/src/ops/function.rs @@ -0,0 +1,304 @@ +/// The version of the call operator that takes an immutable receiver. +/// +/// Instances of `Fn` can be called repeatedly without mutating state. +/// +/// *This trait (`Fn`) is not to be confused with [function pointers] +/// (`fn`).* +/// +/// `Fn` is implemented automatically by closures which only take immutable +/// references to captured variables or don't capture anything at all, as well +/// as (safe) [function pointers] (with some caveats, see their documentation +/// for more details). Additionally, for any type `F` that implements `Fn`, `&F` +/// implements `Fn`, too. +/// +/// Since both [`FnMut`] and [`FnOnce`] are supertraits of `Fn`, any +/// instance of `Fn` can be used as a parameter where a [`FnMut`] or [`FnOnce`] +/// is expected. +/// +/// Use `Fn` as a bound when you want to accept a parameter of function-like +/// type and need to call it repeatedly and without mutating state (e.g., when +/// calling it concurrently). If you do not need such strict requirements, use +/// [`FnMut`] or [`FnOnce`] as bounds. +/// +/// See the [chapter on closures in *The Rust Programming Language*][book] for +/// some more information on this topic. +/// +/// Also of note is the special syntax for `Fn` traits (e.g. +/// `Fn(usize, bool) -> usize`). Those interested in the technical details of +/// this can refer to [the relevant section in the *Rustonomicon*][nomicon]. +/// +/// [book]: ../../book/ch13-01-closures.html +/// [function pointers]: fn +/// [nomicon]: ../../nomicon/hrtb.html +/// +/// # Examples +/// +/// ## Calling a closure +/// +/// ``` +/// let square = |x| x * x; +/// assert_eq!(square(5), 25); +/// ``` +/// +/// ## Using a `Fn` parameter +/// +/// ``` +/// fn call_with_one<F>(func: F) -> usize +/// where F: Fn(usize) -> usize { +/// func(1) +/// } +/// +/// let double = |x| x * 2; +/// assert_eq!(call_with_one(double), 2); +/// ``` +#[lang = "fn"] +#[stable(feature = "rust1", since = "1.0.0")] +#[rustc_diagnostic_item = "Fn"] +#[rustc_paren_sugar] +#[rustc_on_unimplemented( + on( + Args = "()", + note = "wrap the `{Self}` in a closure with no arguments: `|| {{ /* code */ }}`" + ), + on( + _Self = "unsafe fn", + note = "unsafe function cannot be called generically without an unsafe block", + // SAFETY: tidy is not smart enough to tell that the below unsafe block is a string + label = "call the function in a closure: `|| unsafe {{ /* code */ }}`" + ), + message = "expected a `{Fn}<{Args}>` closure, found `{Self}`", + label = "expected an `Fn<{Args}>` closure, found `{Self}`" +)] +#[fundamental] // so that regex can rely that `&str: !FnMut` +#[must_use = "closures are lazy and do nothing unless called"] +pub trait Fn<Args>: FnMut<Args> { + /// Performs the call operation. + #[unstable(feature = "fn_traits", issue = "29625")] + extern "rust-call" fn call(&self, args: Args) -> Self::Output; +} + +/// The version of the call operator that takes a mutable receiver. +/// +/// Instances of `FnMut` can be called repeatedly and may mutate state. +/// +/// `FnMut` is implemented automatically by closures which take mutable +/// references to captured variables, as well as all types that implement +/// [`Fn`], e.g., (safe) [function pointers] (since `FnMut` is a supertrait of +/// [`Fn`]). Additionally, for any type `F` that implements `FnMut`, `&mut F` +/// implements `FnMut`, too. +/// +/// Since [`FnOnce`] is a supertrait of `FnMut`, any instance of `FnMut` can be +/// used where a [`FnOnce`] is expected, and since [`Fn`] is a subtrait of +/// `FnMut`, any instance of [`Fn`] can be used where `FnMut` is expected. +/// +/// Use `FnMut` as a bound when you want to accept a parameter of function-like +/// type and need to call it repeatedly, while allowing it to mutate state. +/// If you don't want the parameter to mutate state, use [`Fn`] as a +/// bound; if you don't need to call it repeatedly, use [`FnOnce`]. +/// +/// See the [chapter on closures in *The Rust Programming Language*][book] for +/// some more information on this topic. +/// +/// Also of note is the special syntax for `Fn` traits (e.g. +/// `Fn(usize, bool) -> usize`). Those interested in the technical details of +/// this can refer to [the relevant section in the *Rustonomicon*][nomicon]. +/// +/// [book]: ../../book/ch13-01-closures.html +/// [function pointers]: fn +/// [nomicon]: ../../nomicon/hrtb.html +/// +/// # Examples +/// +/// ## Calling a mutably capturing closure +/// +/// ``` +/// let mut x = 5; +/// { +/// let mut square_x = || x *= x; +/// square_x(); +/// } +/// assert_eq!(x, 25); +/// ``` +/// +/// ## Using a `FnMut` parameter +/// +/// ``` +/// fn do_twice<F>(mut func: F) +/// where F: FnMut() +/// { +/// func(); +/// func(); +/// } +/// +/// let mut x: usize = 1; +/// { +/// let add_two_to_x = || x += 2; +/// do_twice(add_two_to_x); +/// } +/// +/// assert_eq!(x, 5); +/// ``` +#[lang = "fn_mut"] +#[stable(feature = "rust1", since = "1.0.0")] +#[rustc_diagnostic_item = "FnMut"] +#[rustc_paren_sugar] +#[rustc_on_unimplemented( + on( + Args = "()", + note = "wrap the `{Self}` in a closure with no arguments: `|| {{ /* code */ }}`" + ), + on( + _Self = "unsafe fn", + note = "unsafe function cannot be called generically without an unsafe block", + // SAFETY: tidy is not smart enough to tell that the below unsafe block is a string + label = "call the function in a closure: `|| unsafe {{ /* code */ }}`" + ), + message = "expected a `{FnMut}<{Args}>` closure, found `{Self}`", + label = "expected an `FnMut<{Args}>` closure, found `{Self}`" +)] +#[fundamental] // so that regex can rely that `&str: !FnMut` +#[must_use = "closures are lazy and do nothing unless called"] +pub trait FnMut<Args>: FnOnce<Args> { + /// Performs the call operation. + #[unstable(feature = "fn_traits", issue = "29625")] + extern "rust-call" fn call_mut(&mut self, args: Args) -> Self::Output; +} + +/// The version of the call operator that takes a by-value receiver. +/// +/// Instances of `FnOnce` can be called, but might not be callable multiple +/// times. Because of this, if the only thing known about a type is that it +/// implements `FnOnce`, it can only be called once. +/// +/// `FnOnce` is implemented automatically by closures that might consume captured +/// variables, as well as all types that implement [`FnMut`], e.g., (safe) +/// [function pointers] (since `FnOnce` is a supertrait of [`FnMut`]). +/// +/// Since both [`Fn`] and [`FnMut`] are subtraits of `FnOnce`, any instance of +/// [`Fn`] or [`FnMut`] can be used where a `FnOnce` is expected. +/// +/// Use `FnOnce` as a bound when you want to accept a parameter of function-like +/// type and only need to call it once. If you need to call the parameter +/// repeatedly, use [`FnMut`] as a bound; if you also need it to not mutate +/// state, use [`Fn`]. +/// +/// See the [chapter on closures in *The Rust Programming Language*][book] for +/// some more information on this topic. +/// +/// Also of note is the special syntax for `Fn` traits (e.g. +/// `Fn(usize, bool) -> usize`). Those interested in the technical details of +/// this can refer to [the relevant section in the *Rustonomicon*][nomicon]. +/// +/// [book]: ../../book/ch13-01-closures.html +/// [function pointers]: fn +/// [nomicon]: ../../nomicon/hrtb.html +/// +/// # Examples +/// +/// ## Using a `FnOnce` parameter +/// +/// ``` +/// fn consume_with_relish<F>(func: F) +/// where F: FnOnce() -> String +/// { +/// // `func` consumes its captured variables, so it cannot be run more +/// // than once. +/// println!("Consumed: {}", func()); +/// +/// println!("Delicious!"); +/// +/// // Attempting to invoke `func()` again will throw a `use of moved +/// // value` error for `func`. +/// } +/// +/// let x = String::from("x"); +/// let consume_and_return_x = move || x; +/// consume_with_relish(consume_and_return_x); +/// +/// // `consume_and_return_x` can no longer be invoked at this point +/// ``` +#[lang = "fn_once"] +#[stable(feature = "rust1", since = "1.0.0")] +#[rustc_diagnostic_item = "FnOnce"] +#[rustc_paren_sugar] +#[rustc_on_unimplemented( + on( + Args = "()", + note = "wrap the `{Self}` in a closure with no arguments: `|| {{ /* code */ }}`" + ), + on( + _Self = "unsafe fn", + note = "unsafe function cannot be called generically without an unsafe block", + // SAFETY: tidy is not smart enough to tell that the below unsafe block is a string + label = "call the function in a closure: `|| unsafe {{ /* code */ }}`" + ), + message = "expected a `{FnOnce}<{Args}>` closure, found `{Self}`", + label = "expected an `FnOnce<{Args}>` closure, found `{Self}`" +)] +#[fundamental] // so that regex can rely that `&str: !FnMut` +#[must_use = "closures are lazy and do nothing unless called"] +pub trait FnOnce<Args> { + /// The returned type after the call operator is used. + #[lang = "fn_once_output"] + #[stable(feature = "fn_once_output", since = "1.12.0")] + type Output; + + /// Performs the call operation. + #[unstable(feature = "fn_traits", issue = "29625")] + extern "rust-call" fn call_once(self, args: Args) -> Self::Output; +} + +mod impls { + #[stable(feature = "rust1", since = "1.0.0")] + impl<A, F: ?Sized> Fn<A> for &F + where + F: Fn<A>, + { + extern "rust-call" fn call(&self, args: A) -> F::Output { + (**self).call(args) + } + } + + #[stable(feature = "rust1", since = "1.0.0")] + impl<A, F: ?Sized> FnMut<A> for &F + where + F: Fn<A>, + { + extern "rust-call" fn call_mut(&mut self, args: A) -> F::Output { + (**self).call(args) + } + } + + #[stable(feature = "rust1", since = "1.0.0")] + impl<A, F: ?Sized> FnOnce<A> for &F + where + F: Fn<A>, + { + type Output = F::Output; + + extern "rust-call" fn call_once(self, args: A) -> F::Output { + (*self).call(args) + } + } + + #[stable(feature = "rust1", since = "1.0.0")] + impl<A, F: ?Sized> FnMut<A> for &mut F + where + F: FnMut<A>, + { + extern "rust-call" fn call_mut(&mut self, args: A) -> F::Output { + (*self).call_mut(args) + } + } + + #[stable(feature = "rust1", since = "1.0.0")] + impl<A, F: ?Sized> FnOnce<A> for &mut F + where + F: FnMut<A>, + { + type Output = F::Output; + extern "rust-call" fn call_once(self, args: A) -> F::Output { + (*self).call_mut(args) + } + } +} |