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    // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    /// Entry point of thread panic, for details, see std::macros
    #[macro_export]
    #[allow_internal_unstable]
    #[stable(feature = "core", since = "1.6.0")]
    macro_rules! panic {
        () => (
            panic!("explicit panic")
        );
        ($msg:expr) => ({
            static _MSG_FILE_LINE: (&'static str, &'static str, u32) = ($msg, file!(), line!());
            $crate::panicking::panic(&_MSG_FILE_LINE)
        });
        ($fmt:expr, $($arg:tt)*) => ({
            // The leading _'s are to avoid dead code warnings if this is
            // used inside a dead function. Just `#[allow(dead_code)]` is
            // insufficient, since the user may have
            // `#[forbid(dead_code)]` and which cannot be overridden.
            static _FILE_LINE: (&'static str, u32) = (file!(), line!());
            $crate::panicking::panic_fmt(format_args!($fmt, $($arg)*), &_FILE_LINE)
        });
    }

    /// Ensure that a boolean expression is `true` at runtime.
    ///
    /// This will invoke the `panic!` macro if the provided expression cannot be
    /// evaluated to `true` at runtime.
    ///
    /// This macro has a second version, where a custom panic message can be provided.
    ///
    /// # Examples
    ///
    /// ```
    /// // the panic message for these assertions is the stringified value of the
    /// // expression given.
    /// assert!(true);
    ///
    /// fn some_computation() -> bool { true } // a very simple function
    ///
    /// assert!(some_computation());
    ///
    /// // assert with a custom message
    /// let x = true;
    /// assert!(x, "x wasn't true!");
    ///
    /// let a = 3; let b = 27;
    /// assert!(a + b == 30, "a = {}, b = {}", a, b);
    /// ```
    #[macro_export]
    #[stable(feature = "rust1", since = "1.0.0")]
    macro_rules! assert {
        ($cond:expr) => (
            if !$cond {
                panic!(concat!("assertion failed: ", stringify!($cond)))
            }
        );
        ($cond:expr, $($arg:tt)+) => (
            if !$cond {
                panic!($($arg)+)
            }
        );
    }

    /// Asserts that two expressions are equal to each other.
    ///
    /// On panic, this macro will print the values of the expressions with their
    /// debug representations.
    ///
    /// # Examples
    ///
    /// ```
    /// let a = 3;
    /// let b = 1 + 2;
    /// assert_eq!(a, b);
    /// ```
    #[macro_export]
    #[stable(feature = "rust1", since = "1.0.0")]
    macro_rules! assert_eq {
        ($left:expr , $right:expr) => ({
            match (&($left), &($right)) {
                (left_val, right_val) => {
                    if !(*left_val == *right_val) {
                        panic!("assertion failed: `(left == right)` \
                               (left: `{:?}`, right: `{:?}`)", left_val, right_val)
                    }
                }
            }
        })
    }

    /// Ensure that a boolean expression is `true` at runtime.
    ///
    /// This will invoke the `panic!` macro if the provided expression cannot be
    /// evaluated to `true` at runtime.
    ///
    /// Like `assert!`, this macro also has a second version, where a custom panic
    /// message can be provided.
    ///
    /// Unlike `assert!`, `debug_assert!` statements are only enabled in non
    /// optimized builds by default. An optimized build will omit all
    /// `debug_assert!` statements unless `-C debug-assertions` is passed to the
    /// compiler. This makes `debug_assert!` useful for checks that are too
    /// expensive to be present in a release build but may be helpful during
    /// development.
    ///
    /// # Examples
    ///
    /// ```
    /// // the panic message for these assertions is the stringified value of the
    /// // expression given.
    /// debug_assert!(true);
    ///
    /// fn some_expensive_computation() -> bool { true } // a very simple function
    /// debug_assert!(some_expensive_computation());
    ///
    /// // assert with a custom message
    /// let x = true;
    /// debug_assert!(x, "x wasn't true!");
    ///
    /// let a = 3; let b = 27;
    /// debug_assert!(a + b == 30, "a = {}, b = {}", a, b);
    /// ```
    #[macro_export]
    #[stable(feature = "rust1", since = "1.0.0")]
    macro_rules! debug_assert {
        ($($arg:tt)*) => (if cfg!(debug_assertions) { assert!($($arg)*); })
    }

    /// Asserts that two expressions are equal to each other.
    ///
    /// On panic, this macro will print the values of the expressions with their
    /// debug representations.
    ///
    /// Unlike `assert_eq!`, `debug_assert_eq!` statements are only enabled in non
    /// optimized builds by default. An optimized build will omit all
    /// `debug_assert_eq!` statements unless `-C debug-assertions` is passed to the
    /// compiler. This makes `debug_assert_eq!` useful for checks that are too
    /// expensive to be present in a release build but may be helpful during
    /// development.
    ///
    /// # Examples
    ///
    /// ```
    /// let a = 3;
    /// let b = 1 + 2;
    /// debug_assert_eq!(a, b);
    /// ```
    #[macro_export]
    #[stable(feature = "rust1", since = "1.0.0")]
    macro_rules! debug_assert_eq {
        ($($arg:tt)*) => (if cfg!(debug_assertions) { assert_eq!($($arg)*); })
    }

    /// Helper macro for unwrapping `Result` values while returning early with an
    /// error if the value of the expression is `Err`. Can only be used in
    /// functions that return `Result` because of the early return of `Err` that
    /// it provides.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::io;
    /// use std::fs::File;
    /// use std::io::prelude::*;
    ///
    /// fn write_to_file_using_try() -> Result<(), io::Error> {
    ///     let mut file = try!(File::create("my_best_friends.txt"));
    ///     try!(file.write_all(b"This is a list of my best friends."));
    ///     println!("I wrote to the file");
    ///     Ok(())
    /// }
    /// // This is equivalent to:
    /// fn write_to_file_using_match() -> Result<(), io::Error> {
    ///     let mut file = try!(File::create("my_best_friends.txt"));
    ///     match file.write_all(b"This is a list of my best friends.") {
    ///         Ok(v) => v,
    ///         Err(e) => return Err(e),
    ///     }
    ///     println!("I wrote to the file");
    ///     Ok(())
    /// }
    /// ```
    #[macro_export]
    #[stable(feature = "rust1", since = "1.0.0")]
    macro_rules! try {
        ($expr:expr) => (match $expr {
            $crate::result::Result::Ok(val) => val,
            $crate::result::Result::Err(err) => {
                return $crate::result::Result::Err($crate::convert::From::from(err))
            }
        })
    }

    /// Use the `format!` syntax to write data into a buffer.
    ///
    /// This macro is typically used with a buffer of `&mut `[`Write`][write].
    ///
    /// See [`std::fmt`][fmt] for more information on format syntax.
    ///
    /// [fmt]: ../std/fmt/index.html
    /// [write]: ../std/io/trait.Write.html
    ///
    /// # Examples
    ///
    /// ```
    /// use std::io::Write;
    ///
    /// let mut w = Vec::new();
    /// write!(&mut w, "test").unwrap();
    /// write!(&mut w, "formatted {}", "arguments").unwrap();
    ///
    /// assert_eq!(w, b"testformatted arguments");
    /// ```
    #[macro_export]
    #[stable(feature = "core", since = "1.6.0")]
    macro_rules! write {
        ($dst:expr, $($arg:tt)*) => ($dst.write_fmt(format_args!($($arg)*)))
    }

    /// Use the `format!` syntax to write data into a buffer, appending a newline.
    ///
    /// This macro is typically used with a buffer of `&mut `[`Write`][write].
    ///
    /// See [`std::fmt`][fmt] for more information on format syntax.
    ///
    /// [fmt]: ../std/fmt/index.html
    /// [write]: ../std/io/trait.Write.html
    ///
    /// # Examples
    ///
    /// ```
    /// use std::io::Write;
    ///
    /// let mut w = Vec::new();
    /// writeln!(&mut w, "test").unwrap();
    /// writeln!(&mut w, "formatted {}", "arguments").unwrap();
    ///
    /// assert_eq!(&w[..], "test\nformatted arguments\n".as_bytes());
    /// ```
    #[macro_export]
    #[stable(feature = "rust1", since = "1.0.0")]
    macro_rules! writeln {
        ($dst:expr, $fmt:expr) => (
            write!($dst, concat!($fmt, "\n"))
        );
        ($dst:expr, $fmt:expr, $($arg:tt)*) => (
            write!($dst, concat!($fmt, "\n"), $($arg)*)
        );
    }

    /// A utility macro for indicating unreachable code.
    ///
    /// This is useful any time that the compiler can't determine that some code is unreachable. For
    /// example:
    ///
    /// * Match arms with guard conditions.
    /// * Loops that dynamically terminate.
    /// * Iterators that dynamically terminate.
    ///
    /// # Panics
    ///
    /// This will always panic.
    ///
    /// # Examples
    ///
    /// Match arms:
    ///
    /// ```
    /// # #[allow(dead_code)]
    /// fn foo(x: Option<i32>) {
    ///     match x {
    ///         Some(n) if n >= 0 => println!("Some(Non-negative)"),
    ///         Some(n) if n <  0 => println!("Some(Negative)"),
    ///         Some(_)           => unreachable!(), // compile error if commented out
    ///         None              => println!("None")
    ///     }
    /// }
    /// ```
    ///
    /// Iterators:
    ///
    /// ```
    /// # #[allow(dead_code)]
    /// fn divide_by_three(x: u32) -> u32 { // one of the poorest implementations of x/3
    ///     for i in 0.. {
    ///         if 3*i < i { panic!("u32 overflow"); }
    ///         if x < 3*i { return i-1; }
    ///     }
    ///     unreachable!();
    /// }
    /// ```
    #[macro_export]
    #[stable(feature = "core", since = "1.6.0")]
    macro_rules! unreachable {
        () => ({
            panic!("internal error: entered unreachable code")
        });
        ($msg:expr) => ({
            unreachable!("{}", $msg)
        });
        ($fmt:expr, $($arg:tt)*) => ({
            panic!(concat!("internal error: entered unreachable code: ", $fmt), $($arg)*)
        });
    }

    /// A standardized placeholder for marking unfinished code. It panics with the
    /// message `"not yet implemented"` when executed.
    ///
    /// This can be useful if you are prototyping and are just looking to have your
    /// code typecheck, or if you're implementing a trait that requires multiple
    /// methods, and you're only planning on using one of them.
    ///
    /// # Examples
    ///
    /// Here's an example of some in-progress code. We have a trait `Foo`:
    ///
    /// ```
    /// trait Foo {
    ///     fn bar(&self);
    ///     fn baz(&self);
    /// }
    /// ```
    ///
    /// We want to implement `Foo` on one of our types, but we also want to work on
    /// just `bar()` first. In order for our code to compile, we need to implement
    /// `baz()`, so we can use `unimplemented!`:
    ///
    /// ```
    /// # trait Foo {
    /// #     fn bar(&self);
    /// #     fn baz(&self);
    /// # }
    /// struct MyStruct;
    ///
    /// impl Foo for MyStruct {
    ///     fn bar(&self) {
    ///         // implementation goes here
    ///     }
    ///
    ///     fn baz(&self) {
    ///         // let's not worry about implementing baz() for now
    ///         unimplemented!();
    ///     }
    /// }
    ///
    /// fn main() {
    ///     let s = MyStruct;
    ///     s.bar();
    ///
    ///     // we aren't even using baz() yet, so this is fine.
    /// }
    /// ```
    #[macro_export]
    #[stable(feature = "core", since = "1.6.0")]
    macro_rules! unimplemented {
        () => (panic!("not yet implemented"))
    }

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