maybe_macro 1.0.0

#![deny(missing_docs)]
//! The maybe_macro crate exports one macro, the `maybe!` macro.
//! 
//! The `maybe!` macro makes it neat to construct an option from a value in
//! one line of code if it meets a certain condition. See the macro itself for
//! more documentation about how to use it.

/// The maybe macro.
///
/// This macro takes a name and then an `if` or `if let` statement. If the
/// conditional is true or the pattern matches, the macro evaluates to `Some`.
/// Otherwise, it evaluates to `None`.
///
/// What the macro will evaluate - that comes before the `if` statement - must
/// be an identifier, it can't be any expression.
///
/// # Using with `if`
/// 
/// ```
/// // This will filter out every value greater than 10.
/// slice.iter().filter_map(|&x| maybe!(x if < 10))
/// ```
///
/// # Using with `if let`
///
/// ```
/// // This will filter out all error values.
/// slice.iter().filter_map(|x| maybe!(x if let Ok(_) = x));
/// ```
///
/// Note that ident you return can also come from destructuring in the
/// pattern:
///
/// ```
/// slice.iter().filter_map(|x| maybe!(inner if let Ok(inner) = x));
/// ```
#[macro_export]
macro_rules! maybe {
    ($i:ident if $e:expr)               => {
        if $e { Some($i) } else { None }
    };
    ($i:ident if let $p:pat = $e:expr)  => {
        if let $p = $e { Some($i) } else { None }
    };
}

#[cfg(test)]
mod tests {
    #[test]
    fn conditional() {
        let x = 0;
        let x = maybe!(x if x > 0);
        assert_eq!(x, None);
        let x = 1;
        let x = maybe!(x if x > 0);
        assert_eq!(x, Some(1));
    }

    #[test]
    fn pattern() {
        let x = 0;
        let x = maybe!(x if let 1...10 = x);
        assert_eq!(x, None);
        let x = 1;
        let x = maybe!(x if let 1...10 = x);
        assert_eq!(x, Some(1));
    }

    #[test]
    fn destructure() {
        let x: Result<i32, ()> = Ok(0);
        let x = maybe!(i if let Ok(i) = x);
        assert_eq!(x, Some(0));
    }
}