[Issue 4705] Redesign of std.algorithm.max()/min() + mins()/maxs()

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=4705



--- Comment #5 from bearophile_hugs at eml.cc 2011-01-01 06:33:02 PST ---
Another example to show why a better max() is useful. The task is ot show how
the number less than 1000 which has the longest hailstone sequence. For the
hailstone see:
http://en.wikipedia.org/wiki/Collatz_conjecture

The code, DMD 2.051:

import std.stdio, std.algorithm, std.range, std.typecons;

auto hailstone(int n) {
    auto result = [n];
    while (n != 1) {
        n = n & 1 ? n*3 + 1 : n/2;
        result ~= n;
    }
    return result;
}

void main() {
    auto r = reduce!max(map!((i){return tuple(hailstone(i).length,
i);})(iota(1, 1000)))[1];
    writeln(r);
}


With a max that supports a key function and iterables the line of code in the
main() becomes just:

auto r = max!hailstone(iota(1, 1000));

With the enhancement request 5395 it becomes even more readable:

auto r = max!hailstone(1 .. 1000);

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