Solution: Perform the Calculation

import std.stdio;
enum Operation { add, subtract, multiply, divide }
struct Calculation {
    Operation op;
    double first;
    double second;
}
double[] calculate(Calculation[] calculations...) { 
    double[] results;
    foreach (calculation; calculations) { 
        final switch (calculation.op) {
            case Operation.add:
            results ~= calculation.first + calculation.second; 
            break;
            case Operation.subtract:
            results ~= calculation.first - calculation.second; 
            break;
            case Operation.multiply:
            results ~= calculation.first * calculation.second; 
            break;
            case Operation.divide:
            results ~= calculation.first / calculation.second; 
            break;
        } 
    }
    return results;
}
void main() {
    writeln(calculate(Calculation(Operation.add, 1.1, 2.2),
                      Calculation(Operation.subtract, 3.3, 4.4), 
                      Calculation(Operation.multiply, 5.5, 6.6), 
                      Calculation(Operation.divide, 7.7, 8.8)));
}