Rust macro to conveniently bind temporary value in a chain to a temporary variable

let_chain.rs

// error[E0716]: temporary value dropped while borrowed
//   --> src/main.rs:21:14
//    |
// 21 |     let upper = "abc".to_uppercase().as_str();
//    |                 ^^^^^^^^^^^^^^^^^^^^         - temporary value is freed at the end of this statement
//    |                 |
//    |                 creates a temporary which is freed while still in use
// 22 |     println!("{}", upper);
//    |                    ----- borrow later used here
//    |
// help: consider using a `let` binding to create a longer lived value
//    |
// 21 ~  let binding = "abc".to_uppercase();
// 22 ~  let upper = binding.as_str();
//    |
//
// For more information about this error, try `rustc --explain E0716`.


/// Allows you to write this:
/// ```
/// let_chain!(upper = ("abc".to_uppercase()).as_str());
/// ```
/// instead of
/// ```
/// let binding = "abc".to_uppercase();
/// let upper = binding.as_str();
/// ```
#[macro_export]
macro_rules! let_chain {
    ($name:ident = ($expr:expr)$($chain:tt)*) => (
        let binding = $expr;
        let $name = binding$($chain)*;
    );
    (mut $name:ident = ($expr:expr)$($chain:tt)*) => (
        let binding = $expr;
        let mut $name = binding$($chain)*;
    );
    ($name:ident = (mut $expr:expr)$($chain:tt)*) => (
        let mut binding = $expr;
        let $name = binding$($chain)*;
    );
    (mut $name:ident = (mut $expr:expr)$($chain:tt)*) => (
        let mut binding = $expr;
        let mut $name = binding$($chain)*;
    );
}