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-rw-r--r--tests-integration/Cargo.toml9
-rw-r--r--tests-integration/tests/macros_select.rs33
-rw-r--r--tokio-macros/Cargo.toml1
-rw-r--r--tokio-macros/src/lib.rs13
-rw-r--r--tokio-macros/src/select.rs43
-rw-r--r--tokio/src/future/mod.rs2
-rw-r--r--tokio/src/future/poll_fn.rs4
-rw-r--r--tokio/src/lib.rs17
-rw-r--r--tokio/src/macros/mod.rs9
-rw-r--r--tokio/src/macros/select.rs873
-rw-r--r--tokio/src/macros/support.rs6
-rw-r--r--tokio/src/util/mod.rs8
-rw-r--r--tokio/src/util/rand.rs13
-rw-r--r--tokio/tests/macros_select.rs447
14 files changed, 1468 insertions, 10 deletions
diff --git a/tests-integration/Cargo.toml b/tests-integration/Cargo.toml
index 3cca17a7..6f84afd9 100644
--- a/tests-integration/Cargo.toml
+++ b/tests-integration/Cargo.toml
@@ -6,7 +6,14 @@ edition = "2018"
publish = false
[features]
-full = ["tokio/full", "tokio-test"]
+full = [
+ "macros",
+ "rt-core",
+ "rt-threaded",
+
+ "tokio/full",
+ "tokio-test"
+]
macros = ["tokio/macros"]
rt-core = ["tokio/rt-core"]
rt-threaded = ["rt-core", "tokio/rt-threaded"]
diff --git a/tests-integration/tests/macros_select.rs b/tests-integration/tests/macros_select.rs
new file mode 100644
index 00000000..4c4fef7c
--- /dev/null
+++ b/tests-integration/tests/macros_select.rs
@@ -0,0 +1,33 @@
+#![cfg(feature = "macros")]
+
+use futures::channel::oneshot;
+use futures::executor::block_on;
+use std::thread;
+
+#[test]
+fn join_with_select() {
+ block_on(async {
+ let (tx1, mut rx1) = oneshot::channel::<i32>();
+ let (tx2, mut rx2) = oneshot::channel::<i32>();
+
+ thread::spawn(move || {
+ tx1.send(123).unwrap();
+ tx2.send(456).unwrap();
+ });
+
+ let mut a = None;
+ let mut b = None;
+
+ while a.is_none() || b.is_none() {
+ tokio::select! {
+ v1 = (&mut rx1), if a.is_none() => a = Some(v1.unwrap()),
+ v2 = (&mut rx2), if b.is_none() => b = Some(v2.unwrap()),
+ }
+ }
+
+ let (a, b) = (a.unwrap(), b.unwrap());
+
+ assert_eq!(a, 123);
+ assert_eq!(b, 456);
+ });
+}
diff --git a/tokio-macros/Cargo.toml b/tokio-macros/Cargo.toml
index d69d48d6..3cc3a3e4 100644
--- a/tokio-macros/Cargo.toml
+++ b/tokio-macros/Cargo.toml
@@ -25,6 +25,7 @@ proc-macro = true
[features]
[dependencies]
+proc-macro2 = "1.0.7"
quote = "1"
syn = { version = "1.0.3", features = ["full"] }
diff --git a/tokio-macros/src/lib.rs b/tokio-macros/src/lib.rs
index 09b8b093..17554470 100644
--- a/tokio-macros/src/lib.rs
+++ b/tokio-macros/src/lib.rs
@@ -14,10 +14,11 @@
//! Macros for use with Tokio
-mod entry;
-
extern crate proc_macro;
+mod entry;
+mod select;
+
use proc_macro::TokenStream;
/// Marks async function to be executed by selected runtime.
@@ -198,3 +199,11 @@ pub fn test(args: TokenStream, item: TokenStream) -> TokenStream {
pub fn test_basic(args: TokenStream, item: TokenStream) -> TokenStream {
entry::test(args, item, false)
}
+
+/// Implementation detail of the `select!` macro. This macro is **not** intended
+/// to be used as part of the public API and is permitted to change.
+#[proc_macro]
+#[doc(hidden)]
+pub fn select_priv_declare_output_enum(input: TokenStream) -> TokenStream {
+ select::declare_output_enum(input)
+}
diff --git a/tokio-macros/src/select.rs b/tokio-macros/src/select.rs
new file mode 100644
index 00000000..ddb2e6a0
--- /dev/null
+++ b/tokio-macros/src/select.rs
@@ -0,0 +1,43 @@
+use proc_macro::{TokenStream, TokenTree};
+use proc_macro2::Span;
+use quote::quote;
+use syn::Ident;
+
+pub(crate) fn declare_output_enum(input: TokenStream) -> TokenStream {
+ // passed in is: `(_ _ _)` with one `_` per branch
+ let branches = match input.into_iter().next() {
+ Some(TokenTree::Group(group)) => group.stream().into_iter().count(),
+ _ => panic!("unexpected macro input"),
+ };
+
+ let variants = (0..branches)
+ .map(|num| Ident::new(&format!("_{}", num), Span::call_site()))
+ .collect::<Vec<_>>();
+
+ // Use a bitfield to track which futures completed
+ let mask = Ident::new(
+ if branches <= 8 {
+ "u8"
+ } else if branches <= 16 {
+ "u16"
+ } else if branches <= 32 {
+ "u32"
+ } else if branches <= 64 {
+ "u64"
+ } else {
+ panic!("up to 64 branches supported");
+ },
+ Span::call_site(),
+ );
+
+ TokenStream::from(quote! {
+ pub(super) enum Out<#( #variants ),*> {
+ #( #variants(#variants), )*
+ // Include a `Disabled` variant signifying that all select branches
+ // failed to resolve.
+ Disabled,
+ }
+
+ pub(super) type Mask = #mask;
+ })
+}
diff --git a/tokio/src/future/mod.rs b/tokio/src/future/mod.rs
index 9a155bf7..c5225600 100644
--- a/tokio/src/future/mod.rs
+++ b/tokio/src/future/mod.rs
@@ -6,7 +6,7 @@ mod maybe_done;
pub(crate) use maybe_done::{maybe_done, MaybeDone};
mod poll_fn;
-pub(crate) use poll_fn::poll_fn;
+pub use poll_fn::poll_fn;
mod ready;
pub(crate) use ready::{ok, Ready};
diff --git a/tokio/src/future/poll_fn.rs b/tokio/src/future/poll_fn.rs
index ce2a5524..9b3d1370 100644
--- a/tokio/src/future/poll_fn.rs
+++ b/tokio/src/future/poll_fn.rs
@@ -6,14 +6,14 @@ use std::pin::Pin;
use std::task::{Context, Poll};
/// Future for the [`poll_fn`] function.
-pub(crate) struct PollFn<F> {
+pub struct PollFn<F> {
f: F,
}
impl<F> Unpin for PollFn<F> {}
/// Creates a new future wrapping around a function returning [`Poll`].
-pub(crate) fn poll_fn<T, F>(f: F) -> PollFn<F>
+pub fn poll_fn<T, F>(f: F) -> PollFn<F>
where
F: FnMut(&mut Context<'_>) -> Poll<T>,
{
diff --git a/tokio/src/lib.rs b/tokio/src/lib.rs
index 42a34131..7989d5b3 100644
--- a/tokio/src/lib.rs
+++ b/tokio/src/lib.rs
@@ -282,15 +282,20 @@
//! }
//! ```
-// macros used internally
+// Includes re-exports used by macros.
+//
+// This module is not intended to be part of the public API. In general, any
+// `doc(hidden)` code is not part of Tokio's public and stable API.
#[macro_use]
-mod macros;
+#[doc(hidden)]
+pub mod macros;
cfg_fs! {
pub mod fs;
}
-mod future;
+#[doc(hidden)]
+pub mod future;
pub mod io;
pub mod net;
@@ -333,6 +338,12 @@ cfg_time! {
mod util;
cfg_macros! {
+ /// Implementation detail of the `select!` macro. This macro is **not**
+ /// intended to be used as part of the public API and is permitted to
+ /// change.
+ #[doc(hidden)]
+ pub use tokio_macros::select_priv_declare_output_enum;
+
doc_rt_core! {
cfg_rt_threaded! {
#[cfg(not(test))] // Work around for rust-lang/rust#62127
diff --git a/tokio/src/macros/mod.rs b/tokio/src/macros/mod.rs
index 9136e594..708dd683 100644
--- a/tokio/src/macros/mod.rs
+++ b/tokio/src/macros/mod.rs
@@ -14,4 +14,13 @@ mod loom;
mod ready;
#[macro_use]
+mod select;
+
+#[macro_use]
mod thread_local;
+
+cfg_macros! {
+ // Includes re-exports needed to implement macros
+ #[doc(hidden)]
+ pub mod support;
+}
diff --git a/tokio/src/macros/select.rs b/tokio/src/macros/select.rs
new file mode 100644
index 00000000..00c2c6b5
--- /dev/null
+++ b/tokio/src/macros/select.rs
@@ -0,0 +1,873 @@
+/// Wait on multiple concurrent branches, returning when the **first** branch
+/// completes, cancelling the remaining branches.
+///
+/// The `select` macro accepts one or more branches with the following pattern:
+///
+/// ```text
+/// <pattern> = <async expression> (, if <precondition>)? => <handler>,
+/// ```
+///
+/// Additionally, the `select!` macro may include a single, optional `else`
+/// branch, which evaluates if none of the other branches match their patterns:
+///
+/// ```text
+/// else <expression>
+/// ```
+///
+/// The macro aggregates all `<async expression>` expressions and runs them
+/// concurrently on the **current** task. Once the **first** expression
+/// completes with a value that matches its `<pattern>`, the `select!` macro
+/// returns the result of evaluating the completed branch's `<handler>`
+/// expression.
+///
+/// Additionally, each branch may include an optional `if` precondition. This
+/// precondition is evaluated **before** the <async expression>. If the
+/// precondition returns `false`, the branch is entirely disabled. This
+/// capability is useful when using `select!` within a loop.
+///
+/// The complete lifecycle of a `select!` expression is as follows:
+///
+/// 1. Evaluate all provded `<precondition>` expressions. If the precondition
+/// returns `false`, disable the branch for the remainder of the current call
+/// to `select!`. Re-entering `select!` due to a loop clears the "disabled"
+/// state.
+/// 2. Aggregate the `<async expression>`s from each branch, including the
+/// disabled ones. If the branch is disabled, `<async expression>` is still
+/// evaluated, but the resulting future is not polled.
+/// 3. Concurrently await on the results for all remaining `<async expression>`s.
+/// 4. Once an `<async expression>` returns a value, attempt to apply the value
+/// to the provided `<pattern>`, if the pattern matches, evaluate `<handler>`
+/// and return. If the pattern **does not** match, disable the current branch
+/// and for the remainder of the current call to `select!. Continue from step 3.
+/// 5. If **all** branches are disabled, evaluate the `else` expression. If none
+/// is provided, panic.
+///
+/// # Notes
+///
+/// ### Runtime characteristics
+///
+/// By running all async expressions on the current task, the expressions are
+/// able to run **concurrently** but not in **parallel**. This means all
+/// expressions are run on the same thread and if one branch blocks the thread,
+/// all other expressions will be unable to continue. If parallelism is
+/// required, spawn each async expression using [`tokio::spawn`] and pass the
+/// join handle to `select!`.
+///
+/// [`tokio::spawn`]: crate::spawn
+///
+/// ### Avoid racy `if` preconditions
+///
+/// Given that `if` preconditions are used to disable `select!` branches, some
+/// caution must be used to avoid missing values.
+///
+/// For example, here is **incorrect** usage of `delay` with `if`. The objective
+/// is to repeatedly run an asynchronous task for up to 50 milliseconds.
+/// However, there is a potential for the `delay` completion to be missed.
+///
+/// ```no_run
+/// use tokio::time::{self, Duration};
+///
+/// async fn some_async_work() {
+/// // do work
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+/// let mut delay = time::delay_for(Duration::from_millis(50));
+///
+/// while !delay.is_elapsed() {
+/// tokio::select! {
+/// _ = &mut delay, if !delay.is_elapsed() => {
+/// println!("operation timed out");
+/// }
+/// _ = some_async_work() => {
+/// println!("operation completed");
+/// }
+/// }
+/// }
+/// }
+/// ```
+///
+/// In the above example, `delay.is_elapsed()` may return `true` even if
+/// `delay.poll()` never returned `Ready`. This opens up a potential race
+/// condition where `delay` expires between the `while !delay.is_elapsed()`
+/// check and the call to `select!` resulting in the `some_async_work()` call to
+/// run uninterrupted despite the delay having elapsed.
+///
+/// One way to write the above example without the race would be:
+///
+/// ```
+/// use tokio::time::{self, Duration};
+///
+/// async fn some_async_work() {
+/// # time::delay_for(Duration::from_millis(10)).await;
+/// // do work
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+/// let mut delay = time::delay_for(Duration::from_millis(50));
+///
+/// loop {
+/// tokio::select! {
+/// _ = &mut delay => {
+/// println!("operation timed out");
+/// break;
+/// }
+/// _ = some_async_work() => {
+/// println!("operation completed");
+/// }
+/// }
+/// }
+/// }
+/// ```
+///
+/// ### Fairness
+///
+/// `select!` randomly picks a branch to check first. This provides some level
+/// of fairness when calling `select!` in a loop with branches that are always
+/// ready.
+///
+/// # Panics
+///
+/// `select!` panics if all branches are disabled **and** there is no provided
+/// `else` branch. A branch is disabled when the provided `if` precondition
+/// returns `false` **or** when the pattern does not match the result of `<async
+/// expression>.
+///
+/// # Examples
+///
+/// Basic select with two branches.
+///
+/// ```
+/// async fn do_stuff_async() {
+/// // async work
+/// }
+///
+/// async fn more_async_work() {
+/// // more here
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+/// tokio::select! {
+/// _ = do_stuff_async() => {
+/// println!("do_stuff_async() completed first")
+/// }
+/// _ = more_async_work() => {
+/// println!("more_async_work() completed first")
+/// }
+/// };
+/// }
+///
+/// ```
+///
+/// Basic stream selecting.
+///
+/// ```
+/// use tokio::stream::{self, StreamExt};
+///
+/// #[tokio::main]
+/// async fn main() {
+/// let mut stream1 = stream::iter(vec![1, 2, 3]);
+/// let mut stream2 = stream::iter(vec![4, 5, 6]);
+///
+/// let next = tokio::select! {
+/// v = stream1.next() => v.unwrap(),
+/// v = stream2.next() => v.unwrap(),
+/// };
+///
+/// assert!(next == 1 || next == 4);
+/// }
+/// ```
+///
+/// Collect the contents of two streams. In this example, we rely on pattern
+/// matching and the fact that `stream::iter` is "fused", i.e. once the stream
+/// is complete, all calls to `next()` return `None`.
+///
+/// ```
+/// use tokio::stream::{self, StreamExt};
+///
+/// #[tokio::main]
+/// async fn main() {
+/// let mut stream1 = stream::iter(vec![1, 2, 3]);
+/// let mut stream2 = stream::iter(vec![4, 5, 6]);
+///
+/// let mut values = vec![];
+///
+/// loop {
+/// tokio::select! {
+/// Some(v) = stream1.next() => values.push(v),
+/// Some(v) = stream2.next() => values.push(v),
+/// else => break,
+/// }
+/// }
+///
+/// values.sort();
+/// assert_eq!(&[1, 2, 3, 4, 5, 6], &values[..]);
+/// }
+/// ```
+///
+/// Using the same future in multiple select! expressions can be done by passing
+/// a reference to the future. Doing so requires the future to be [`Unpin`]. A
+/// future can be made [`Unpin`] by either using [`Box::pin`] or stack pinning.
+///
+/// [`Unpin`]: std::marker::Unpin
+/// [`Box::pin`]: std::boxed::Box::pin
+///
+/// Here, a stream is consumed for at most 1 second.
+///
+/// ```
+/// use tokio::stream::{self, StreamExt};
+/// use tokio::time::{self, Duration};
+///
+/// #[tokio::main]
+/// async fn main() {
+/// let mut stream = stream::iter(vec![1, 2, 3]);
+/// let mut delay = time::delay_for(Duration::from_secs(1));
+///
+/// loop {
+/// tokio::select! {
+/// maybe_v = stream.next() => {
+/// if let Some(v) = maybe_v {
+/// println!("got = {}", v);
+/// } else {
+/// break;
+/// }
+/// }
+/// _ = &mut delay => {
+/// println!("timeout");
+/// break;
+/// }
+/// }
+/// }
+/// }
+/// ```
+///
+/// Joining two values using `select!`.
+///
+/// ```
+/// use tokio::sync::oneshot;
+///
+/// #[tokio::main]
+/// async fn main() {
+/// let (tx1, mut rx1) = oneshot::channel();
+/// let (tx2, mut rx2) = oneshot::channel();
+///
+/// tokio::spawn(async move {
+/// tx1.send("first").unwrap();
+/// });
+///
+/// tokio::spawn(async move {
+/// tx2.send("second").unwrap();
+/// });
+///
+/// let mut a = None;
+/// let mut b = None;
+///
+/// while a.is_none() || b.is_none() {
+/// tokio::select! {
+/// v1 = (&mut rx1), if a.is_none() => a = Some(v1.unwrap()),
+/// v2 = (&mut rx2), if b.is_none() => b = Some(v2.unwrap()),
+/// }
+/// }
+///
+/// let res = (a.unwrap(), b.unwrap());
+///
+/// assert_eq!(res.0, "first");
+/// assert_eq!(res.1, "second");
+/// }
+/// ```
+#[macro_export]
+macro_rules! select {
+ // Uses a declarative macro to do **most** of the work. While it is possible
+ // to implement fully with a declarative macro, a procedural macro is used
+ // to enable improved error messages.
+ //
+ // The macro is structured as a tt-muncher. All branches are processed and
+ // normalized. Once the input is normalized, it is passed to the top-most
+ // rule. When entering the macro, `@{ }` is inserted at the front. This is
+ // used to collect the normalized input.
+ //
+ // The macro only recurses once per branch. This allows using `select!`
+ // without requiring the user to increase the recursion limit.
+
+ // All input is normalized, now transform.
+ (@ {
+ // One `_` for each branch in the `select!` macro. Passing this to
+ // `count!` converts $skip to an integer.
+ ( $($count:tt)* )
+
+ // Normalized select branches. `( $skip )` is a set of `_` characters.
+ // There is one `_` for each select branch **before** this one. Given
+ // that all input futures are stored in a tuple, $skip is useful for
+ // generating a pattern to reference the future for the current branch.
+ // $skip is also used as an argument to `count!`, returning the index of
+ // the current select branch.
+ $( ( $($skip:tt)* ) $bind:pat = $fut:expr, if $c:expr => $handle:expr, )+
+
+ // Fallback expression used when all select branches have been disabled.
+ ; $else:expr
+
+ }) => {{
+ // Enter a context where stable "function-like" proc macros can be used.
+ //
+ // This module is defined within a scope and should not leak out of this
+ // macro.
+ mod util {
+ // Generate an enum with one variant per select branch
+ $crate::select_priv_declare_output_enum!( ( $($count)* ) );
+ }
+
+ // `tokio::macros::support` is a public, but doc(hidden) module
+ // including a re-export of all types needed by this macro.
+ use $crate::macros::support::Future;
+ use $crate::macros::support::Pin;
+ use $crate::macros::support::Poll::{Ready, Pending};
+
+ const BRANCHES: u32 = $crate::count!( $($count)* );
+
+ let mut disabled: util::Mask = Default::default();
+
+ // First, invoke all the pre-conditions. For any that return true,
+ // set the appropriate bit in `disabled`.
+ $(
+ if !$c {
+ let mask = 1 << $crate::count!( $($skip)* );
+ disabled |= mask;
+ }
+ )*
+
+ // Create a scope to separate polling from handling the output. This
+ // adds borrow checker flexibility when using the macro.
+ let mut output = {
+ // Safety: Nothing must be moved out of `futures`. This is to
+ // satisfy the requirement of `Pin::new_unchecked` called below.
+ let mut futures = ( $( $fut , )+ );
+
+ $crate::macros::support::poll_fn(|cx| {
+ // Track if any branch returns pending. If no branch completes
+ // **or** returns pending, this implies that all branches are
+ // disabled.
+ let mut is_pending = false;
+
+ // Randomly generate a starting point. This makes `select!` a
+ // bit more fair and avoids always polling the first future.
+ let start = $crate::macros::support::thread_rng_n(BRANCHES);
+
+ for i in 0..BRANCHES {
+ let branch = (start + i) % BRANCHES;
+
+ match branch {
+ $(
+ $crate::count!( $($skip)* ) => {
+ // First, if the future has previously been
+ // disabled, do not poll it again. This is done
+ // by checking the associated bit in the
+ // `disabled` bit field.
+ let mask = 1 << branch;
+
+ if disabled & mask == mask {
+ // The future has been disabled.
+ continue;
+ }
+
+ // Extract the future for this branch from the
+ // tuple
+ let ( $($skip,)* fut, .. ) = &mut futures;
+
+ // Safety: future is stored on the stack above
+ // and never moved.
+ let mut fut = unsafe { Pin::new_unchecked(fut) };
+
+ // Try polling it
+ let out = match fut.poll(cx) {
+ Ready(out) => out,
+ Pending => {
+ // Track that at least one future is
+ // still pending and continue polling.
+ is_pending = true;
+ continue;
+ }
+ };
+
+ // Disable the future from future polling.
+ disabled |= mask;
+
+ // The future returned a value, check if matches
+ // the specified pattern.
+ #[allow(unused_variables)]
+ match &out {
+ $bind => {}
+ _ => continue,
+ }
+
+ // The select is complete, return the value
+ return Ready($crate::select_variant!(util::Out, ($($skip)*))(out));
+ }
+ )*
+ _ => unreachable!("reaching this means there probably is an off by one bug"),
+ }
+ }
+
+ if is_pending {
+ Pending
+ } else {
+ // All branches have been disabled.
+ Ready(util::Out::Disabled)
+ }
+ }).await
+ };
+
+ match output {
+ $(
+ $crate::select_variant!(util::Out, ($($skip)*) ($bind)) => $handle,
+ )*
+ util::Out::Disabled => $else,
+ _ => unreachable!("failed to match bind"),
+ }
+ }};
+
+ // ==== Normalize =====
+
+ // These rules match a single `select!` branch and normalize it for
+ // processing by the first rule.
+
+ (@ { $($t:tt)* } ) => {
+ // No `else` branch
+ $crate::select!(@{ $($t)*; unreachable!() })
+ };
+ (@ { $($t:tt)* } else => $else:expr $(,)?) => {
+ $crate::select!(@{ $($t)*; $else })
+ };
+ (@ { ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr, if $c:expr => $h:block, $($r:tt)* ) => {
+ $crate::select!(@{ ($($s)* _) $($t)* ($($s)*) $p = $f, if $c => $h, } $($r)*)
+ };
+ (@ { ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr => $h:block, $($r:tt)* ) => {
+ $crate::select!(@{ ($($s)* _) $($t)* ($($s)*) $p = $f, if true => $h, } $($r)*)
+ };
+ (@ { ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr, if $c:expr => $h:block $($r:tt)* ) => {
+ $crate::select!(@{ ($($s)* _) $($t)* ($($s)*) $p = $f, if $c => $h, } $($r)*)
+ };
+ (@ { ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr => $h:block $($r:tt)* ) => {
+ $crate::select!(@{ ($($s)* _) $($t)* ($($s)*) $p = $f, if true => $h, } $($r)*)
+ };
+ (@ { ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr, if $c:expr => $h:expr ) => {
+ $crate::select!(@{ ($($s)* _) $($t)* ($($s)*) $p = $f, if $c => $h, })
+ };
+ (@ { ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr => $h:expr ) => {
+ $crate::select!(@{ ($($s)* _) $($t)* ($($s)*) $p = $f, if true => $h, })
+ };
+ (@ { ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr, if $c:expr => $h:expr, $($r:tt)* ) => {
+ $crate::select!(@{ ($($s)* _) $($t)* ($($s)*) $p = $f, if $c => $h, } $($r)*)
+ };
+ (@ { ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr => $h:expr, $($r:tt)* ) => {
+ $crate::select!(@{ ($($s)* _) $($t)* ($($s)*) $p = $f, if true => $h, } $($r)*)
+ };
+
+ // ===== Entry point =====
+
+ ( $p:pat = $($t:tt)* ) => {
+ $crate::select!(@{ () } $p = $($t)*)
+ };
+ () => {
+ compile_error!("select! requires at least one branch.")
+ };
+}
+
+// And here... we manually list out matches for up to 64 branches... I'm not
+// happy about it either, but this is how we manage to use a declarative macro!
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! count {
+ () => {
+ 0
+ };
+ (_) => {
+ 1
+ };
+ (_ _) => {
+ 2
+ };
+ (_ _ _) => {
+ 3
+ };
+ (_ _ _ _) => {
+ 4
+ };
+ (_ _ _ _ _) => {
+ 5
+ };
+ (_ _ _ _ _ _) => {
+ 6
+ };
+ (_ _ _ _ _ _ _) => {
+ 7
+ };
+ (_ _ _ _ _ _ _ _) => {
+ 8
+ };
+ (_ _ _ _ _ _ _ _ _) => {
+ 9
+ };
+ (_ _ _ _ _ _ _ _ _ _) => {
+ 10
+ };
+ (_ _ _ _ _ _ _ _ _ _ _) => {
+ 11
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _) => {
+ 12
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 13
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 14
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 15
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 16
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 17
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 18
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 19
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 20
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 21
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 22
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 23
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 24
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 25
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 26
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 27
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 28
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 29
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 30
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 31
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 32
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 33
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 34
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 35
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 36
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 37
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 38
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 39
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 40
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 41
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 42
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 43
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 44
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 45
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 46
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 47
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 48
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 49
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 50
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 51
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 52
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 53
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 54
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 55
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 56
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 57
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 58
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 59
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 60
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 61
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 62
+ };
+ (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+ 63
+ };
+}
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! select_variant {
+ ($($p:ident)::*, () $($t:tt)*) => {
+ $($p)::*::_0 $($t)*
+ };
+ ($($p:ident)::*, (_) $($t:tt)*) => {
+ $($p)::*::_1 $($t)*
+ };
+ ($($p:ident)::*, (_ _) $($t:tt)*) => {
+ $($p)::*::_2 $($t)*
+ };
+ ($($p:ident)::*, (_ _ _) $($t:tt)*) => {
+ $($p)::*::_3 $($t)*
+ };
+ ($($p:ident)::*, (_ _ _ _) $($t:tt)*) => {
+ $($p)::*::_4 $($t)*
+ };
+ ($($p:ident)::*, (_ _ _ _ _) $($t:tt)*) => {
+ $($p)::*::_5 $($t)*
+ };
+ ($($p:ident)::*, (_ _ _ _ _ _) $($t:tt)*) => {
+ $($p)::*::_6 $($t)*
+ };
+ ($($p:ident)::*, (_ _ _ _ _ _ _) $($t:tt)*) => {
+ $($p)::*::_7 $($t)*
+ };
+ ($($p:ident)::*, (_ _ _ _ _ _ _ _) $($t:tt)*) => {
+ $($p)::*::_8 $($t)*
+ };
+ ($($p:ident)::*, (_ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+ $($p)::*::_9 $($t)*
+ };
+ ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+ $($p)::*::_10 $($t)*
+ };
+ ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+ $($p)::*::_11 $($t)*
+ };
+ ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+ $($p)::*::_12 $($t)*
+ };
+ ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+ $($p)::*::_13 $($t)*
+ };
+ ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+ $($p)::*::_14 $($t)*
+ };
+ ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:t