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/// Prints and returns the value of a given expression for quick and dirty
/// debugging.
///
/// Like [`std::dbg`], but uses [`crate::Debug`], so has nicer output.
///
/// An example:
///
/// ```rust
/// let a = 2;
/// let b = dbg!(a * 2) + 1;
/// // ^-- prints: [src/main.rs:2] a * 2 = 4
/// assert_eq!(b, 5);
/// ```
///
/// The macro works by using the `Debug` implementation of the type of
/// the given expression to print the value to [stderr] along with the
/// source location of the macro invocation as well as the source code
/// of the expression.
///
/// Invoking the macro on an expression moves and takes ownership of it
/// before returning the evaluated expression unchanged. If the type
/// of the expression does not implement `Copy` and you don't want
/// to give up ownership, you can instead borrow with `dbg!(&expr)`
/// for some expression `expr`.
///
/// The `dbg!` macro works exactly the same in release builds.
/// This is useful when debugging issues that only occur in release
/// builds or when debugging in release mode is significantly faster.
///
/// Note that the macro is intended as a debugging tool and therefore you
/// should avoid having uses of it in version control for long periods
/// (other than in tests and similar).
/// Debug output from production code is better done with other facilities
/// such as the [`debug!`] macro from the [`log`] crate.
///
/// # Stability
///
/// The exact output printed by this macro should not be relied upon
/// and is subject to future changes.
///
/// # Panics
///
/// Panics if writing to `io::stderr` fails.
///
/// # Differences to [`std::dbg`]
///
/// When invoked on multiple items, the output is grouped, to be clearer in
/// loops.
///
/// ```rust
/// let x = [1, 2, 3];
/// for i in 0..x.len() {
/// dbg!(i, x[i]);
/// }
/// ```
///
/// Will print with [`std::dbg`]
///
/// ```text
/// [examples\macro.rs:11] i = 0
/// [examples\macro.rs:11] x[i] = 1
/// [examples\macro.rs:11] i = 1
/// [examples\macro.rs:11] x[i] = 2
/// [examples\macro.rs:11] i = 2
/// [examples\macro.rs:11] x[i] = 3
/// ```
///
/// But this will print
///
/// ```text
/// [examples\macro.rs:10] (i, x[i]) = (0, 1)
/// [examples\macro.rs:10] (i, x[i]) = (1, 2)
/// [examples\macro.rs:10] (i, x[i]) = (2, 3)
/// ```
///
/// # Further examples
///
/// With a method call:
///
/// ```rust
/// fn foo(n: usize) {
/// if let Some(_) = dbg!(n.checked_sub(4)) {
/// // ...
/// }
/// }
///
/// foo(3)
/// ```
///
/// This prints to [stderr]:
///
/// ```text,ignore
/// [src/main.rs:4] n.checked_sub(4) = None
/// ```
///
/// Naive factorial implementation:
///
/// ```rust
/// fn factorial(n: u32) -> u32 {
/// if dbg!(n <= 1) {
/// dbg!(1)
/// } else {
/// dbg!(n * factorial(n - 1))
/// }
/// }
///
/// dbg!(factorial(4));
/// ```
///
/// This prints to [stderr]:
///
/// ```text,ignore
/// [src/main.rs:3] n <= 1 = false
/// [src/main.rs:3] n <= 1 = false
/// [src/main.rs:3] n <= 1 = false
/// [src/main.rs:3] n <= 1 = true
/// [src/main.rs:4] 1 = 1
/// [src/main.rs:5] n * factorial(n - 1) = 2
/// [src/main.rs:5] n * factorial(n - 1) = 6
/// [src/main.rs:5] n * factorial(n - 1) = 24
/// [src/main.rs:11] factorial(4) = 24
/// ```
///
/// The `dbg!(..)` macro moves the input:
///
/// ```compile_fail
/// /// A wrapper around `usize` which importantly is not Copyable.
/// #[derive(Debug)]
/// struct NoCopy(usize);
///
/// let a = NoCopy(42);
/// let _ = dbg!(a); // <-- `a` is moved here.
/// let _ = dbg!(a); // <-- `a` is moved again; error!
/// ```
///
/// You can also use `dbg!()` without a value to just print the
/// file and line whenever it's reached.
///
/// Finally, if you want to `dbg!(..)` multiple values, it will treat them as
/// a tuple (and return it, too):
///
/// ```
/// assert_eq!(dbg!(1usize, 2u32), (1, 2));
/// ```
///
/// However, a single argument with a trailing comma will still not be treated
/// as a tuple, following the convention of ignoring trailing commas in macro
/// invocations. You can use a 1-tuple directly if you need one:
///
/// ```
/// assert_eq!(1, dbg!(1u32,)); // trailing comma ignored
/// assert_eq!((1,), dbg!((1u32,))); // 1-tuple
/// ```
///
///
///
/// [stderr]: https://en.wikipedia.org/wiki/Standard_streams#Standard_error_(stderr)
/// [`debug!`]: https://docs.rs/log/*/log/macro.debug.html
/// [`log`]: https://crates.io/crates/log