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// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! Standard library macros
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//!
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//! This modules contains a set of macros which are exported from the standard
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//! library. Each macro is available for use when linking against the standard
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//! library.
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/// The entry point for panic of Rust threads.
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///
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/// This macro is used to inject panic into a Rust thread, causing the thread to
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/// panic entirely. Each thread's panic can be reaped as the `Box<Any>` type,
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/// and the single-argument form of the `panic!` macro will be the value which
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/// is transmitted.
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///
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/// The multi-argument form of this macro panics with a string and has the
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/// `format!` syntax for building a string.
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///
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/// # Examples
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///
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/// ```should_panic
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/// # #![allow(unreachable_code)]
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/// panic!();
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/// panic!("this is a terrible mistake!");
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/// panic!(4); // panic with the value of 4 to be collected elsewhere
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/// panic!("this is a {} {message}", "fancy", message = "message");
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/// ```
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#[macro_export]
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#[stable(feature = "rust1", since = "1.0.0")]
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#[allow_internal_unstable]
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macro_rules! panic {
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() => ({
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panic!("explicit panic")
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});
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($msg:expr) => ({
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$crate::rt::begin_panic($msg, {
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// static requires less code at runtime, more constant data
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static _FILE_LINE_COL: (&'static str, u32, u32) = (file!(), line!(), column!());
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&_FILE_LINE_COL
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})
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});
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($fmt:expr, $($arg:tt)+) => ({
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$crate::rt::begin_panic_fmt(&format_args!($fmt, $($arg)+), {
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// The leading _'s are to avoid dead code warnings if this is
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// used inside a dead function. Just `#[allow(dead_code)]` is
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// insufficient, since the user may have
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// `#[forbid(dead_code)]` and which cannot be overridden.
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static _FILE_LINE_COL: (&'static str, u32, u32) = (file!(), line!(), column!());
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&_FILE_LINE_COL
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})
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});
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}
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/// Macro for printing to the standard output.
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///
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/// Equivalent to the `println!` macro except that a newline is not printed at
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/// the end of the message.
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///
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/// Note that stdout is frequently line-buffered by default so it may be
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/// necessary to use `io::stdout().flush()` to ensure the output is emitted
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/// immediately.
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///
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/// # Panics
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///
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/// Panics if writing to `io::stdout()` fails.
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///
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/// # Examples
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///
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/// ```
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/// use std::io::{self, Write};
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///
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/// print!("this ");
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/// print!("will ");
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/// print!("be ");
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/// print!("on ");
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/// print!("the ");
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/// print!("same ");
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/// print!("line ");
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///
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/// io::stdout().flush().unwrap();
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///
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/// print!("this string has a newline, why not choose println! instead?\n");
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///
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/// io::stdout().flush().unwrap();
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/// ```
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#[macro_export]
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#[stable(feature = "rust1", since = "1.0.0")]
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#[allow_internal_unstable]
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macro_rules! print {
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($($arg:tt)*) => ($crate::io::_print(format_args!($($arg)*)));
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}
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/// Macro for printing to the standard output, with a newline. On all
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/// platforms, the newline is the LINE FEED character (`\n`/`U+000A`) alone
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/// (no additional CARRIAGE RETURN (`\r`/`U+000D`).
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///
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/// Use the `format!` syntax to write data to the standard output.
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/// See `std::fmt` for more information.
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///
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/// # Panics
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///
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/// Panics if writing to `io::stdout()` fails.
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///
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/// # Examples
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///
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/// ```
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/// println!();
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/// println!("hello there!");
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/// println!("format {} arguments", "some");
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/// ```
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#[macro_export]
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#[stable(feature = "rust1", since = "1.0.0")]
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macro_rules! println {
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() => (print!("\n"));
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($fmt:expr) => (print!(concat!($fmt, "\n")));
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($fmt:expr, $($arg:tt)*) => (print!(concat!($fmt, "\n"), $($arg)*));
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}
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/// A macro to select an event from a number of receivers.
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///
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/// This macro is used to wait for the first event to occur on a number of
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/// receivers. It places no restrictions on the types of receivers given to
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/// this macro, this can be viewed as a heterogeneous select.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(mpsc_select)]
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///
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/// use std::thread;
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/// use std::sync::mpsc;
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///
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/// // two placeholder functions for now
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/// fn long_running_thread() {}
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/// fn calculate_the_answer() -> u32 { 42 }
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///
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/// let (tx1, rx1) = mpsc::channel();
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/// let (tx2, rx2) = mpsc::channel();
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///
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/// thread::spawn(move|| { long_running_thread(); tx1.send(()).unwrap(); });
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/// thread::spawn(move|| { tx2.send(calculate_the_answer()).unwrap(); });
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///
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/// select! {
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/// _ = rx1.recv() => println!("the long running thread finished first"),
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/// answer = rx2.recv() => {
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/// println!("the answer was: {}", answer.unwrap());
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/// }
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/// }
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/// # drop(rx1.recv());
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/// # drop(rx2.recv());
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/// ```
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///
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/// For more information about select, see the `std::sync::mpsc::Select` structure.
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#[macro_export]
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#[unstable(feature = "mpsc_select", issue = "27800")]
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macro_rules! select {
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(
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$($name:pat = $rx:ident.$meth:ident() => $code:expr),+
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) => ({
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use $crate::sync::mpsc::Select;
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let sel = Select::new();
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$( let mut $rx = sel.handle(&$rx); )+
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unsafe {
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$( $rx.add(); )+
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}
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let ret = sel.wait();
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$( if ret == $rx.id() { let $name = $rx.$meth(); $code } else )+
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{ unreachable!() }
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})
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}
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#[cfg(test)]
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macro_rules! assert_approx_eq {
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($a:expr, $b:expr) => ({
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let (a, b) = (&$a, &$b);
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assert!((*a - *b).abs() < 1.0e-6,
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"{} is not approximately equal to {}", *a, *b);
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})
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}
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/// Built-in macros to the compiler itself.
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///
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/// These macros do not have any corresponding definition with a `macro_rules!`
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/// macro, but are documented here. Their implementations can be found hardcoded
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/// into libsyntax itself.
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#[cfg(dox)]
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pub mod builtin {
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/// The core macro for formatted string creation & output.
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///
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/// This macro produces a value of type [`fmt::Arguments`]. This value can be
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/// passed to the functions in [`std::fmt`] for performing useful functions.
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/// All other formatting macros ([`format!`], [`write!`], [`println!`], etc) are
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/// proxied through this one.
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///
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/// For more information, see the documentation in [`std::fmt`].
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///
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/// [`fmt::Arguments`]: ../std/fmt/struct.Arguments.html
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/// [`std::fmt`]: ../std/fmt/index.html
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/// [`format!`]: ../std/macro.format.html
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/// [`write!`]: ../std/macro.write.html
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/// [`println!`]: ../std/macro.println.html
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///
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/// # Examples
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///
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/// ```
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/// use std::fmt;
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///
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/// let s = fmt::format(format_args!("hello {}", "world"));
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/// assert_eq!(s, format!("hello {}", "world"));
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///
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[macro_export]
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macro_rules! format_args { ($fmt:expr, $($args:tt)*) => ({
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/* compiler built-in */
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}) }
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/// Inspect an environment variable at compile time.
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///
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/// This macro will expand to the value of the named environment variable at
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/// compile time, yielding an expression of type `&'static str`.
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///
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/// If the environment variable is not defined, then a compilation error
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/// will be emitted. To not emit a compile error, use the `option_env!`
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/// macro instead.
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///
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/// # Examples
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///
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/// ```
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/// let path: &'static str = env!("PATH");
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/// println!("the $PATH variable at the time of compiling was: {}", path);
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[macro_export]
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macro_rules! env { ($name:expr) => ({ /* compiler built-in */ }) }
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/// Optionally inspect an environment variable at compile time.
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///
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/// If the named environment variable is present at compile time, this will
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/// expand into an expression of type `Option<&'static str>` whose value is
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/// `Some` of the value of the environment variable. If the environment
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/// variable is not present, then this will expand to `None`.
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///
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/// A compile time error is never emitted when using this macro regardless
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/// of whether the environment variable is present or not.
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///
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/// # Examples
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///
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/// ```
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/// let key: Option<&'static str> = option_env!("SECRET_KEY");
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/// println!("the secret key might be: {:?}", key);
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[macro_export]
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macro_rules! option_env { ($name:expr) => ({ /* compiler built-in */ }) }
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/// Concatenate identifiers into one identifier.
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///
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/// This macro takes any number of comma-separated identifiers, and
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/// concatenates them all into one, yielding an expression which is a new
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/// identifier. Note that hygiene makes it such that this macro cannot
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/// capture local variables. Also, as a general rule, macros are only
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/// allowed in item, statement or expression position. That means while
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/// you may use this macro for referring to existing variables, functions or
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/// modules etc, you cannot define a new one with it.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(concat_idents)]
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///
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/// # fn main() {
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/// fn foobar() -> u32 { 23 }
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///
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/// let f = concat_idents!(foo, bar);
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/// println!("{}", f());
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///
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/// // fn concat_idents!(new, fun, name) { } // not usable in this way!
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/// # }
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/// ```
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#[unstable(feature = "concat_idents_macro", issue = "29599")]
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#[macro_export]
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macro_rules! concat_idents {
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($($e:ident),*) => ({ /* compiler built-in */ })
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}
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/// Concatenates literals into a static string slice.
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///
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/// This macro takes any number of comma-separated literals, yielding an
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/// expression of type `&'static str` which represents all of the literals
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/// concatenated left-to-right.
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///
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/// Integer and floating point literals are stringified in order to be
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/// concatenated.
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///
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/// # Examples
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///
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/// ```
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/// let s = concat!("test", 10, 'b', true);
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/// assert_eq!(s, "test10btrue");
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[macro_export]
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macro_rules! concat { ($($e:expr),*) => ({ /* compiler built-in */ }) }
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/// A macro which expands to the line number on which it was invoked.
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///
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/// The expanded expression has type `u32`, and the returned line is not
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/// the invocation of the `line!()` macro itself, but rather the first macro
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/// invocation leading up to the invocation of the `line!()` macro.
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///
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/// # Examples
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///
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/// ```
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/// let current_line = line!();
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/// println!("defined on line: {}", current_line);
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[macro_export]
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macro_rules! line { () => ({ /* compiler built-in */ }) }
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/// A macro which expands to the column number on which it was invoked.
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///
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/// The expanded expression has type `u32`, and the returned column is not
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/// the invocation of the `column!()` macro itself, but rather the first macro
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/// invocation leading up to the invocation of the `column!()` macro.
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///
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/// # Examples
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///
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/// ```
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/// let current_col = column!();
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/// println!("defined on column: {}", current_col);
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[macro_export]
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macro_rules! column { () => ({ /* compiler built-in */ }) }
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/// A macro which expands to the file name from which it was invoked.
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///
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/// The expanded expression has type `&'static str`, and the returned file
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/// is not the invocation of the `file!()` macro itself, but rather the
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/// first macro invocation leading up to the invocation of the `file!()`
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/// macro.
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///
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/// # Examples
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///
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/// ```
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/// let this_file = file!();
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/// println!("defined in file: {}", this_file);
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[macro_export]
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macro_rules! file { () => ({ /* compiler built-in */ }) }
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/// A macro which stringifies its argument.
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///
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/// This macro will yield an expression of type `&'static str` which is the
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/// stringification of all the tokens passed to the macro. No restrictions
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/// are placed on the syntax of the macro invocation itself.
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///
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/// Note that the expanded results of the input tokens may change in the
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/// future. You should be careful if you rely on the output.
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///
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/// # Examples
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///
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/// ```
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/// let one_plus_one = stringify!(1 + 1);
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/// assert_eq!(one_plus_one, "1 + 1");
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[macro_export]
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macro_rules! stringify { ($t:tt) => ({ /* compiler built-in */ }) }
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/// Includes a utf8-encoded file as a string.
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///
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/// The file is located relative to the current file. (similarly to how
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/// modules are found)
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///
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/// This macro will yield an expression of type `&'static str` which is the
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/// contents of the file.
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///
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/// # Examples
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///
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/// ```rust,ignore
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/// let secret_key = include_str!("secret-key.ascii");
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[macro_export]
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macro_rules! include_str { ($file:expr) => ({ /* compiler built-in */ }) }
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/// Includes a file as a reference to a byte array.
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///
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/// The file is located relative to the current file. (similarly to how
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/// modules are found)
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///
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/// This macro will yield an expression of type `&'static [u8; N]` which is
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/// the contents of the file.
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///
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/// # Examples
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///
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/// ```rust,ignore
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/// let secret_key = include_bytes!("secret-key.bin");
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[macro_export]
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macro_rules! include_bytes { ($file:expr) => ({ /* compiler built-in */ }) }
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/// Expands to a string that represents the current module path.
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///
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/// The current module path can be thought of as the hierarchy of modules
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/// leading back up to the crate root. The first component of the path
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/// returned is the name of the crate currently being compiled.
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///
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/// # Examples
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///
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/// ```
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/// mod test {
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/// pub fn foo() {
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/// assert!(module_path!().ends_with("test"));
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/// }
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/// }
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///
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/// test::foo();
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[macro_export]
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macro_rules! module_path { () => ({ /* compiler built-in */ }) }
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/// Boolean evaluation of configuration flags.
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///
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/// In addition to the `#[cfg]` attribute, this macro is provided to allow
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/// boolean expression evaluation of configuration flags. This frequently
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/// leads to less duplicated code.
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///
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/// The syntax given to this macro is the same syntax as [the `cfg`
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/// attribute](../reference.html#conditional-compilation).
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///
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/// # Examples
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///
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/// ```
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/// let my_directory = if cfg!(windows) {
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/// "windows-specific-directory"
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/// } else {
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/// "unix-directory"
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/// };
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[macro_export]
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macro_rules! cfg { ($($cfg:tt)*) => ({ /* compiler built-in */ }) }
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/// Parse a file as an expression or an item according to the context.
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///
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/// The file is located relative to the current file. (similarly to how
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/// modules are found)
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///
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/// Using this macro is often a bad idea, because if the file is
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/// parsed as an expression, it is going to be placed in the
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/// surrounding code unhygenically. This could result in variables
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/// or functions being different from what the file expected if
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/// there are variables or functions that have the same name in
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/// the current file.
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///
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/// # Examples
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///
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/// ```ignore
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/// fn foo() {
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/// include!("/path/to/a/file")
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/// }
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[macro_export]
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macro_rules! include { ($file:expr) => ({ /* compiler built-in */ }) }
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}
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