generic_array/
functional.rs

1//! Functional programming with generic sequences
2//!
3//! Please see `tests/generics.rs` for examples of how to best use these in your generic functions.
4
5use core::iter::FromIterator;
6
7use crate::sequence::*;
8
9/// Defines the relationship between one generic sequence and another,
10/// for operations such as `map` and `zip`.
11pub trait MappedGenericSequence<T, U>: GenericSequence<T> {
12    /// Mapped sequence type
13    type Mapped: GenericSequence<U, Length = Self::Length>;
14}
15
16impl<'a, T, U, S: MappedGenericSequence<T, U>> MappedGenericSequence<T, U> for &'a S
17where
18    &'a S: GenericSequence<T>,
19    S: GenericSequence<T, Length = <&'a S as GenericSequence<T>>::Length>,
20{
21    type Mapped = <S as MappedGenericSequence<T, U>>::Mapped;
22}
23
24impl<'a, T, U, S: MappedGenericSequence<T, U>> MappedGenericSequence<T, U> for &'a mut S
25where
26    &'a mut S: GenericSequence<T>,
27    S: GenericSequence<T, Length = <&'a mut S as GenericSequence<T>>::Length>,
28{
29    type Mapped = <S as MappedGenericSequence<T, U>>::Mapped;
30}
31
32/// Mapped type for a generic sequence
33pub type Mapped<S, T, U> = <S as MappedGenericSequence<T, U>>::Mapped;
34
35/// Accessor type for a mapped generic sequence
36///
37/// NOTE: The choice to use the `Sequence` associated type here instead of `Mapped`
38/// is due to only the `Sequence` type being guaranteed to implement `FromIterator`.
39/// However, this does lead to some oddity where `FallibleGenericSequence::from_fallible_iter`
40/// is implemented on `Mapped`, but returns the `Sequence`/`MappedSequence` type. Same difference, though.
41pub type MappedSequence<S, T, U> = <Mapped<S, T, U> as GenericSequence<U>>::Sequence;
42
43/// Defines functional programming methods for generic sequences
44pub trait FunctionalSequence<T>: GenericSequence<T> {
45    /// Maps a `GenericSequence` to another `GenericSequence`.
46    ///
47    /// If the mapping function panics, any already initialized elements in the new sequence
48    /// will be dropped, AND any unused elements in the source sequence will also be dropped.
49    #[inline(always)]
50    fn map<U, F>(self, f: F) -> MappedSequence<Self, T, U>
51    where
52        Self: MappedGenericSequence<T, U>,
53        F: FnMut(Self::Item) -> U,
54    {
55        FromIterator::from_iter(self.into_iter().map(f))
56    }
57
58    /// Tries to map a `GenericSequence` to another `GenericSequence`, returning a `Result`.
59    ///
60    /// If the mapping function errors or panics, any already initialized elements in the new sequence
61    /// will be dropped, AND any unused elements in the source sequence will also be dropped.
62    #[inline(always)]
63    fn try_map<U, F, E>(self, f: F) -> Result<MappedSequence<Self, T, U>, E>
64    where
65        Self: MappedGenericSequence<T, U>,
66        MappedSequence<Self, T, U>: FromFallibleIterator<U>,
67        F: FnMut(Self::Item) -> Result<U, E>,
68    {
69        FromFallibleIterator::from_fallible_iter(self.into_iter().map(f))
70    }
71
72    /// Combines two `GenericSequence` instances and iterates through both of them,
73    /// initializing a new `GenericSequence` with the result of the zipped mapping function.
74    ///
75    /// If the mapping function panics, any already initialized elements in the new sequence
76    /// will be dropped, AND any unused elements in the source sequences will also be dropped.
77    ///
78    /// **WARNING**: If using the `alloc` crate feature, mixing stack-allocated
79    /// `GenericArray<T, N>` and heap-allocated `Box<GenericArray<T, N>>` within [`zip`](FunctionalSequence::zip)
80    /// should be done with care or avoided.
81    ///
82    /// For copy-types, it could be easy to accidentally move the array
83    /// out of the `Box` when zipping with a stack-allocated array, which could cause a stack-overflow
84    /// if the array is sufficiently large. However, that being said, the second where clause
85    /// ensuring they map to the same sequence type will catch common errors, such as:
86    ///
87    /// ```compile_fail
88    /// # use generic_array::{*, functional::FunctionalSequence};
89    /// # #[cfg(feature = "alloc")]
90    /// fn test() {
91    ///     let stack = arr![1, 2, 3, 4];
92    ///     let heap = box_arr![5, 6, 7, 8];
93    ///     let mixed = stack.zip(heap, |a, b| a + b);
94    ///     //                --- ^^^^ expected struct `GenericArray`, found struct `Box`
95    /// }
96    /// # #[cfg(not(feature = "alloc"))]
97    /// # compile_error!("requires alloc feature to test this properly");
98    /// ```
99    #[inline(always)]
100    fn zip<B, Rhs, U, F>(self, rhs: Rhs, f: F) -> MappedSequence<Self, T, U>
101    where
102        Self: MappedGenericSequence<T, U>,
103        Rhs: MappedGenericSequence<B, U, Mapped = MappedSequence<Self, T, U>>,
104        Rhs: GenericSequence<B, Length = Self::Length>,
105        F: FnMut(Self::Item, Rhs::Item) -> U,
106    {
107        rhs.inverted_zip2(self, f)
108    }
109
110    /// Folds (or reduces) a sequence of data into a single value.
111    ///
112    /// If the fold function panics, any unused elements will be dropped.
113    #[inline(always)]
114    fn fold<U, F>(self, init: U, f: F) -> U
115    where
116        F: FnMut(U, Self::Item) -> U,
117    {
118        self.into_iter().fold(init, f)
119    }
120
121    /// Folds (or reduces) a sequence of data into a single value, returning a `Result`.
122    ///
123    /// If the fold function errors or panics, any unused elements will be dropped.
124    #[inline(always)]
125    fn try_fold<U, E, F>(self, init: U, f: F) -> Result<U, E>
126    where
127        F: FnMut(U, Self::Item) -> Result<U, E>,
128    {
129        self.into_iter().try_fold(init, f)
130    }
131}
132
133impl<'a, T, S: GenericSequence<T>> FunctionalSequence<T> for &'a S where &'a S: GenericSequence<T> {}
134
135impl<'a, T, S: GenericSequence<T>> FunctionalSequence<T> for &'a mut S where
136    &'a mut S: GenericSequence<T>
137{
138}
generic_array/functional.rs

generic_array/
functional.rs
