std::ranges::for_each

Example

Sum: @struct type = {
    operator(): (inout this, n: int) = { sum += n; }
    sum: int = 0;
}

main: () = {
    nums: std::vector = (3, 4, 2, 8, 15, 267);
 
    printer:= :(n) = { std::cout << " (n)$"; };
 
    ranges: namespace == std::ranges;
    std::cout << "before:";
    ranges::for_each(std::as_const(nums), printer);
    printer('\n');
 
    ranges::for_each(nums, :(inout n: int) = n++);
 
    // calls Sum::operator() for each number
    res:= ranges::for_each(nums.begin(), nums.end(), Sum());
    assert(res.in == nums.end());
 
    std::cout << "after: ";
    ranges::for_each(nums.cbegin(), nums.cend(), printer);
 
    std::cout << "\nsum: (res.fun.sum)$\n";
 
    pair: type == std::pair<int, std::string>; 
    pairs: std::vector = (:pair=(1,"one"), :pair=(2,"two"), :pair=(3,"three"));
 
    std::cout << "project the pair::first: ";
    ranges::for_each(pairs, printer, :(p: pair) -> int = { return p.first; });
 
    std::cout << "\nproject the pair::second:";
    ranges::for_each(pairs, printer, pair::second&);
    printer('\n');
}

Output

before: 3 4 2 8 15 267 
after:  4 5 3 9 16 268
sum: 305
project the pair::first:  1 2 3
project the pair::second: one two three 