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//! Thread-safe by-reference variant of [`Foldable`](crate::classes::Foldable).
//!
//! **User story:** "I want to fold over a thread-safe memoized value by reference."
//!
//! ### Examples
//!
//! ```
//! use fp_library::{
//! brands::*,
//! classes::send_ref_foldable::*,
//! types::*,
//! };
//!
//! let lazy = ArcLazy::new(|| 10);
//! let result = send_ref_fold_map::<ArcFnBrand, LazyBrand<ArcLazyConfig>, _, _>(
//! |a: &i32| a.to_string(),
//! &lazy,
//! );
//! assert_eq!(result, "10");
//! ```
#[fp_macros::document_module]
mod inner {
use {
crate::{
classes::{
send_clone_fn::SendLiftFn,
*,
},
kinds::*,
types::{
Dual,
SendEndofunction,
},
},
fp_macros::*,
};
/// Thread-safe by-reference folding over a structure.
///
/// Similar to [`RefFoldable`], but closures and elements must be `Send + Sync`.
/// Unlike [`ParRefFunctor`](crate::classes::ParRefFunctor) (which requires
/// [`RefFunctor`](crate::classes::RefFunctor) as a supertrait), `SendRefFoldable`
/// does not require `RefFoldable`. This is because the SendRef monadic traits
/// (functor, pointed, lift, applicative) construct new containers internally,
/// and `ArcLazy::new` requires `Send` on closures, which `Ref` trait signatures
/// do not guarantee. The SendRef and Ref hierarchies are therefore independent.
///
/// All three methods (`send_ref_fold_map`, `send_ref_fold_right`, `send_ref_fold_left`)
/// have default implementations in terms of each other, so implementors
/// only need to provide one.
#[kind(type Of<'a, A: 'a>: 'a;)]
pub trait SendRefFoldable {
/// Maps values to a monoid by reference and combines them (thread-safe).
#[document_signature]
#[document_type_parameters(
"The lifetime of the elements.",
"The brand of the cloneable function to use.",
"The type of the elements.",
"The monoid type."
)]
#[document_parameters(
"The function to map each element reference to a monoid. Must be `Send + Sync`.",
"The structure to fold."
)]
#[document_returns("The combined monoid value.")]
#[document_examples]
///
/// ```
/// use fp_library::{
/// brands::*,
/// classes::send_ref_foldable::*,
/// types::*,
/// };
///
/// let lazy = ArcLazy::new(|| 5);
/// let result = send_ref_fold_map::<ArcFnBrand, LazyBrand<ArcLazyConfig>, _, _>(
/// |a: &i32| a.to_string(),
/// &lazy,
/// );
/// assert_eq!(result, "5");
/// ```
fn send_ref_fold_map<'a, FnBrand, A: Send + Sync + 'a + Clone, M>(
func: impl Fn(&A) -> M + Send + Sync + 'a,
fa: &Apply!(<Self as Kind!( type Of<'a, T: 'a>: 'a; )>::Of<'a, A>),
) -> M
where
FnBrand: SendLiftFn + 'a,
M: Monoid + Send + Sync + 'a, {
Self::send_ref_fold_right::<FnBrand, A, M>(
move |a: &A, acc| Semigroup::append(func(a), acc),
Monoid::empty(),
fa,
)
}
/// Folds the structure from the right by reference (thread-safe).
#[document_signature]
#[document_type_parameters(
"The lifetime of the elements.",
"The brand of the cloneable function to use.",
"The type of the elements.",
"The type of the accumulator."
)]
#[document_parameters(
"The function to apply to each element reference and accumulator. Must be `Send + Sync`.",
"The initial value of the accumulator.",
"The structure to fold."
)]
#[document_returns("The final accumulator value.")]
#[document_examples]
///
/// ```
/// use fp_library::{
/// brands::*,
/// classes::send_ref_foldable::SendRefFoldable,
/// types::*,
/// };
///
/// let lazy = ArcLazy::new(|| 10);
/// let result = <LazyBrand<ArcLazyConfig> as SendRefFoldable>::send_ref_fold_right::<
/// ArcFnBrand,
/// _,
/// _,
/// >(|a: &i32, acc: i32| acc + *a, 0, &lazy);
/// assert_eq!(result, 10);
/// ```
fn send_ref_fold_right<'a, FnBrand, A: Send + Sync + 'a + Clone, B: Send + Sync + 'a>(
func: impl Fn(&A, B) -> B + Send + Sync + 'a,
initial: B,
fa: &Apply!(<Self as Kind!( type Of<'a, T: 'a>: 'a; )>::Of<'a, A>),
) -> B
where
FnBrand: SendLiftFn + 'a, {
let f = <FnBrand as SendLiftFn>::new(move |(a, b): (A, B)| func(&a, b));
let m = Self::send_ref_fold_map::<FnBrand, A, SendEndofunction<FnBrand, B>>(
move |a: &A| {
let a = a.clone();
let f = f.clone();
SendEndofunction::<FnBrand, B>::new(<FnBrand as SendLiftFn>::new(move |b| {
let a = a.clone();
f((a, b))
}))
},
fa,
);
m.0(initial)
}
/// Folds the structure from the left by reference (thread-safe).
#[document_signature]
#[document_type_parameters(
"The lifetime of the elements.",
"The brand of the cloneable function to use.",
"The type of the elements.",
"The type of the accumulator."
)]
#[document_parameters(
"The function to apply to the accumulator and each element reference. Must be `Send + Sync`.",
"The initial value of the accumulator.",
"The structure to fold."
)]
#[document_returns("The final accumulator value.")]
#[document_examples]
///
/// ```
/// use fp_library::{
/// brands::*,
/// classes::send_ref_foldable::SendRefFoldable,
/// types::*,
/// };
///
/// let lazy = ArcLazy::new(|| 10);
/// let result = <LazyBrand<ArcLazyConfig> as SendRefFoldable>::send_ref_fold_left::<
/// ArcFnBrand,
/// _,
/// _,
/// >(|acc: i32, a: &i32| acc + *a, 0, &lazy);
/// assert_eq!(result, 10);
/// ```
fn send_ref_fold_left<'a, FnBrand, A: Send + Sync + 'a + Clone, B: Send + Sync + 'a>(
func: impl Fn(B, &A) -> B + Send + Sync + 'a,
initial: B,
fa: &Apply!(<Self as Kind!( type Of<'a, T: 'a>: 'a; )>::Of<'a, A>),
) -> B
where
FnBrand: SendLiftFn + 'a, {
let f = <FnBrand as SendLiftFn>::new(move |(b, a): (B, A)| func(b, &a));
let m = Self::send_ref_fold_map::<FnBrand, A, Dual<SendEndofunction<FnBrand, B>>>(
move |a: &A| {
let a = a.clone();
let f = f.clone();
Dual(SendEndofunction::<FnBrand, B>::new(<FnBrand as SendLiftFn>::new(
move |b| {
let a = a.clone();
f((b, a))
},
)))
},
fa,
);
(m.0).0(initial)
}
}
/// Maps values to a monoid by reference and combines them (thread-safe).
///
/// Free function version that dispatches to [the type class' associated function][`SendRefFoldable::send_ref_fold_map`].
#[document_signature]
#[document_type_parameters(
"The lifetime of the elements.",
"The brand of the cloneable function to use.",
"The brand of the structure.",
"The type of the elements.",
"The monoid type."
)]
#[document_parameters(
"The function to map each element reference to a monoid.",
"The structure to fold."
)]
#[document_returns("The combined monoid value.")]
#[document_examples]
///
/// ```
/// use fp_library::{
/// brands::*,
/// classes::send_ref_foldable::*,
/// types::*,
/// };
///
/// let lazy = ArcLazy::new(|| 5);
/// let result = send_ref_fold_map::<ArcFnBrand, LazyBrand<ArcLazyConfig>, _, _>(
/// |a: &i32| a.to_string(),
/// &lazy,
/// );
/// assert_eq!(result, "5");
/// ```
pub fn send_ref_fold_map<
'a,
FnBrand: SendLiftFn + 'a,
Brand: SendRefFoldable,
A: Send + Sync + 'a + Clone,
M,
>(
func: impl Fn(&A) -> M + Send + Sync + 'a,
fa: &Apply!(<Brand as Kind!( type Of<'a, T: 'a>: 'a; )>::Of<'a, A>),
) -> M
where
M: Monoid + Send + Sync + 'a, {
Brand::send_ref_fold_map::<FnBrand, A, M>(func, fa)
}
}
pub use inner::*;