Macro for_each

macro_rules! for_each {
    ($pattern:pat in $($rem:tt)*) => { ... };
}

Iterates over all elements of an iterator, const equivalent of Iterator::for_each

Iterator methods

This macro supports emulating iterator methods by expanding to equivalent code.

The supported iterator methods are documented in the iterator_dsl module, because they are also supported by other konst::iter macros.

Examples

Custom iterator

use konst::iter::{IntoIterKind, IsIteratorKind};

struct Upto10(u8);

impl IntoIterKind for Upto10 { type Kind = IsIteratorKind; }

impl Upto10 {
    const fn next(mut self) -> Option<(u8, Self)> {
        if self.0 < 10 {
            let ret = self.0;
            self.0 += 1;
            Some((ret, self))
        } else {
            None
        }
    }
}

const N: u32 = {
    let mut n = 0u32;
    konst::iter::for_each!{elem in Upto10(7) =>
        n = n * 10 + elem as u32;
    }
    n
};

assert_eq!(N, 789);

Summing pairs

This example requires the "rust_1_51" feature, because it uses const generics.

use konst::iter::for_each;
     
const fn add_pairs<const N: usize>(l: [u32; N], r: [u32; N]) -> [u32; N] {
    let mut out = [0u32; N];

    for_each!{(i, val) in &l,zip(&r),map(|(l, r)| *l + *r),enumerate() =>
        out[i] = val;
    }

    out
}

assert_eq!(add_pairs([], []), []);
assert_eq!(add_pairs([3], [5]), [8]);
assert_eq!(add_pairs([3, 5], [8, 13]), [11, 18]);