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//! A newtype wrapper whose [`Semigroup`](crate::classes::Semigroup) instance always keeps the last
//! (rightmost) value.
//!
//! ### Examples
//!
//! ```
//! use fp_library::{
//! functions::*,
//! types::Last,
//! };
//!
//! assert_eq!(append(Last(1), Last(2)), Last(2));
//! ```
#[fp_macros::document_module]
mod inner {
use {
crate::classes::*,
fp_macros::*,
};
/// A newtype wrapper whose [`Semigroup`] instance always keeps the last value.
///
/// `append(Last(a), Last(b))` returns `Last(b)`, discarding `a`.
///
/// There is no [`Monoid`] instance because there is no identity element.
#[document_examples]
///
/// ```
/// use fp_library::{
/// functions::*,
/// types::Last,
/// };
///
/// assert_eq!(append(Last("hello"), Last("world")), Last("world"));
/// ```
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[derive(Clone, Copy, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct Last<A>(
/// The wrapped value.
pub A,
);
#[document_type_parameters("The wrapped type.")]
impl<A> Semigroup for Last<A> {
/// Returns the last (rightmost) value, discarding the first.
#[document_signature]
///
#[document_parameters("The first value (discarded).", "The second value (kept).")]
///
#[document_returns("The second value.")]
#[document_examples]
///
/// ```
/// use fp_library::{
/// functions::*,
/// types::Last,
/// };
///
/// assert_eq!(append(Last(1), Last(2)), Last(2));
/// ```
fn append(
_a: Self,
b: Self,
) -> Self {
b
}
}
}
pub use inner::*;
#[cfg(test)]
mod tests {
use {
super::*,
crate::functions::*,
quickcheck_macros::quickcheck,
};
#[quickcheck]
fn semigroup_associativity(
a: i32,
b: i32,
c: i32,
) -> bool {
let x = Last(a);
let y = Last(b);
let z = Last(c);
append(x, append(y, z)) == append(append(x, y), z)
}
}