fold()

import std.stdio;
import std.algorithm; // fold()

void main()
{
    int[] numbers = [1, 2, 3, 4, 5];

    // numbers cannot be empty; the 1st element is the seed
    int result1 = numbers.fold!("a * b");
    int result2 = numbers.fold!((a, b) => a * b);

    // numbers can be empty; the provided value (1) is the seed
    int result3 = numbers.fold!("a * b")(1);
    int result4 = numbers.fold!((a, b) => a * b)(1);

    writeln(result1); // 120
    writeln(result2); // 120
    writeln(result3); // 120
    writeln(result4); // 120
}