fmt-tools 0.1.0

Provides various tools for creating objects that implement `Debug` and `Display` traits.
Documentation 
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use core::fmt::{self, Debug, Display, Formatter};

/// Implements [`Debug`] and [`Display`] based on a function object.
pub struct FmtFn<F>
where
    F: ?Sized,
{
    values_fn: F,
}

impl<F> FmtFn<F> {
    const fn new(values_fn: F) -> Self {
        Self { values_fn }
    }
}

impl<F> Display for FmtFn<F>
where
    F: Fn(&mut Formatter) -> fmt::Result + ?Sized,
{
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        (self.values_fn)(f)
    }
}

impl<F> Debug for FmtFn<F>
where
    F: Fn(&mut Formatter) -> fmt::Result + ?Sized,
{
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        (self.values_fn)(f)
    }
}

/// Creates an object that implements [`Debug`] and [`Display`] based on the provided function object.
///
/// Example:
///
/// ```rust
/// let fmt = fmt_tools::fmt_fn(|f| f.write_str("foo"));
///
/// assert_eq!(format!("{fmt:?}"), "foo");
/// assert_eq!(format!("{fmt}"), "foo");
/// ```
pub const fn fmt_fn<F>(f: F) -> FmtFn<F>
where
    F: Fn(&mut Formatter) -> fmt::Result,
{
    FmtFn::new(f)
}

#[cfg(test)]
mod tests {
    use super::FmtFn;
    use core::fmt::{self, Formatter};

    #[test]
    fn test_fmt_fn() {
        let fmt = super::fmt_fn(|f| f.write_str("foo"));

        assert_eq!(std::format!("{fmt:?}"), "foo");
        assert_eq!(std::format!("{fmt}"), "foo");
    }

    #[test]
    fn test_coerce_unsized() {
        let fmt: &FmtFn<dyn Fn(&mut Formatter) -> fmt::Result> = &super::fmt_fn(|f| f.write_str("foo"));

        assert_eq!(std::format!("{fmt:?}"), "foo");
        assert_eq!(std::format!("{fmt}"), "foo");
    }
}