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//! Types that can be mapped over by receiving references to their contents,
//! with thread-safe mapping functions.
//!
//! ### Examples
//!
//! ```
//! use fp_library::{
//! brands::*,
//! functions::*,
//! types::*,
//! };
//!
//! let memo = ArcLazy::new(|| 10);
//! let mapped = send_ref_map::<LazyBrand<ArcLazyConfig>, _, _>(|x: &i32| *x * 2, &memo);
//! assert_eq!(*mapped.evaluate(), 20);
//! ```
#[fp_macros::document_module]
mod inner {
use {
crate::kinds::*,
fp_macros::*,
};
/// A type class for types that can be mapped over, receiving references, with thread-safe functions.
///
/// This is a variant of [`RefFunctor`](crate::classes::RefFunctor) where the mapping function
/// must be `Send`, making it suitable for thread-safe lazy types like
/// [`ArcLazy`](crate::types::ArcLazy).
///
/// ### Why a Separate Trait?
///
/// A single trait with `Send` bounds on `RefFunctor` would exclude `RcLazy`, which uses
/// `Rc` (a `!Send` type). By keeping `RefFunctor` free of `Send` bounds and providing
/// `SendRefFunctor` separately, `RcLazy` can implement `RefFunctor` while `ArcLazy`
/// implements only `SendRefFunctor`.
///
/// ### Laws
///
/// `SendRefFunctor` instances must satisfy the following laws:
/// * Identity: `send_ref_map(|x| x.clone(), fa)` evaluates to a value equal to `fa`'s evaluated value.
/// * Composition: `send_ref_map(|x| f(&g(x)), fa)` evaluates to the same value as `send_ref_map(f, send_ref_map(g, fa))`.
#[document_examples]
///
/// SendRefFunctor laws for [`ArcLazy`](crate::types::ArcLazy):
///
/// ```
/// use fp_library::{
/// brands::*,
/// functions::*,
/// types::*,
/// };
///
/// // Identity: send_ref_map(|x| x.clone(), fa) evaluates to the same value as fa.
/// let fa = ArcLazy::pure(5);
/// let mapped = send_ref_map::<LazyBrand<ArcLazyConfig>, _, _>(|x: &i32| *x, &fa);
/// assert_eq!(*mapped.evaluate(), *fa.evaluate());
///
/// // Composition: send_ref_map(|x| f(&g(x)), fa) = send_ref_map(f, send_ref_map(g, fa))
/// let f = |x: &i32| x + 1;
/// let g = |x: &i32| *x * 2;
/// let fa = ArcLazy::pure(5);
/// let composed = send_ref_map::<LazyBrand<ArcLazyConfig>, _, _>(|x: &i32| f(&g(x)), &fa);
/// let sequential = send_ref_map::<LazyBrand<ArcLazyConfig>, _, _>(
/// f,
/// &send_ref_map::<LazyBrand<ArcLazyConfig>, _, _>(g, &fa),
/// );
/// assert_eq!(*composed.evaluate(), *sequential.evaluate());
/// ```
///
/// # Cache chain behavior
///
/// Chaining `send_ref_map` calls on memoized types like [`ArcLazy`](crate::types::ArcLazy)
/// creates a linked list of `Arc`-referenced cells. Each mapped value retains a reference to
/// its predecessor, so the entire chain of predecessor cells stays alive as long as any
/// downstream mapped value is reachable. Be aware that long chains can accumulate memory
/// that is only freed when the final value in the chain is dropped.
///
/// # Why `Fn` (not `FnOnce`)?
///
/// The `func` parameter uses `Fn` rather than `FnOnce` for consistency
/// with [`RefFunctor`](crate::classes::RefFunctor), which requires `Fn`
/// to support multi-element containers like `Vec`. Closures that move
/// out of their captures (`FnOnce` but not `Fn`) cannot be used with
/// `send_ref_map`; these are rare and can be restructured by extracting
/// the move into a surrounding scope.
#[kind(type Of<'a, A: 'a>: 'a;)]
pub trait SendRefFunctor {
/// Maps a thread-safe function over the values in the functor context, where the function takes a reference.
#[document_signature]
///
#[document_type_parameters(
"The lifetime of the values.",
"The type of the value(s) inside the functor.",
"The type of the result(s) of applying the function."
)]
///
#[document_parameters(
"The function to apply to the value(s) inside the functor.",
"The functor instance containing the value(s)."
)]
///
#[document_returns(
"A new functor instance containing the result(s) of applying the function."
)]
#[document_examples]
///
/// ```
/// use fp_library::{
/// brands::*,
/// classes::*,
/// types::*,
/// };
///
/// let memo = ArcLazy::new(|| 10);
/// let mapped = LazyBrand::<ArcLazyConfig>::send_ref_map(|x: &i32| *x * 2, &memo);
/// assert_eq!(*mapped.evaluate(), 20);
/// ```
fn send_ref_map<'a, A: Send + Sync + 'a, B: Send + Sync + 'a>(
func: impl Fn(&A) -> B + Send + 'a,
fa: &Apply!(<Self as Kind!( type Of<'a, T: 'a>: 'a; )>::Of<'a, A>),
) -> Apply!(<Self as Kind!( type Of<'a, T: 'a>: 'a; )>::Of<'a, B>);
}
/// Maps a thread-safe function over the values in the functor context, where the function takes a reference.
///
/// Free function version that dispatches to [the type class' associated function][`SendRefFunctor::send_ref_map`].
#[document_signature]
///
#[document_type_parameters(
"The lifetime of the values.",
"The brand of the functor.",
"The type of the value(s) inside the functor.",
"The type of the result(s) of applying the function."
)]
///
#[document_parameters(
"The function to apply to the value(s) inside the functor.",
"The functor instance containing the value(s)."
)]
///
#[document_returns("A new functor instance containing the result(s) of applying the function.")]
#[document_examples]
///
/// ```
/// use fp_library::{
/// brands::*,
/// functions::*,
/// types::*,
/// };
///
/// let memo = ArcLazy::new(|| 10);
/// let mapped = send_ref_map::<LazyBrand<ArcLazyConfig>, _, _>(|x: &i32| *x * 2, &memo);
/// assert_eq!(*mapped.evaluate(), 20);
/// ```
pub fn send_ref_map<'a, Brand: SendRefFunctor, A: Send + Sync + 'a, B: Send + Sync + 'a>(
func: impl Fn(&A) -> B + Send + 'a,
fa: &Apply!(<Brand as Kind!( type Of<'a, T: 'a>: 'a; )>::Of<'a, A>),
) -> Apply!(<Brand as Kind!( type Of<'a, T: 'a>: 'a; )>::Of<'a, B>) {
Brand::send_ref_map(func, fa)
}
}
pub use inner::*;
#[cfg(test)]
mod tests {
use {
crate::{
brands::*,
functions::*,
types::*,
},
quickcheck_macros::quickcheck,
};
/// SendRefFunctor identity law: send_ref_map(Clone::clone, lazy) evaluates to the same value as lazy.
#[quickcheck]
fn prop_send_ref_functor_identity(x: i32) -> bool {
let lazy = ArcLazy::pure(x);
let mapped = send_ref_map::<LazyBrand<ArcLazyConfig>, _, _>(|v: &i32| *v, &lazy);
*mapped.evaluate() == *lazy.evaluate()
}
/// SendRefFunctor composition law: send_ref_map(|x| g(&f(x)), lazy) == send_ref_map(g, send_ref_map(f, lazy)).
#[quickcheck]
fn prop_send_ref_functor_composition(x: i32) -> bool {
let f = |v: &i32| v.wrapping_mul(2);
let g = |v: &i32| v.wrapping_add(1);
let lazy1 = ArcLazy::pure(x);
let lazy2 = ArcLazy::pure(x);
let composed = send_ref_map::<LazyBrand<ArcLazyConfig>, _, _>(|v: &i32| g(&f(v)), &lazy1);
let sequential = send_ref_map::<LazyBrand<ArcLazyConfig>, _, _>(
g,
&send_ref_map::<LazyBrand<ArcLazyConfig>, _, _>(f, &lazy2),
);
*composed.evaluate() == *sequential.evaluate()
}
}