rational

1 auto r = rational(10, 2);       // If you called rational(n, d), value is reduced.
2 assert(r.num == 5);             // 10 / 2 => 5 / 1
3 assert(r.den == 1);
4 
5 assert(r == rational(5));       // rational(5) == rational(5, 1)
6 
7 assert(r == 5.over(1));          // UFCS : n.over(d) == n.rational(d) == rational(n, d)
8 
9 r *= -1.over(5);
10 assert(r.num == -1);            // If rational value is negative, numerator is always negative.
11 assert(r.den == 1);             // But denominator is always positive.
12 assert(r == rational(1, 1));    // (5 / 1) * (1 / 5) == (1 / 1)
13 assert(r == 1);                 // Can check equality to T by "==" operator.
14 assert(r > 2);                  // Also comparison operator.
15 
16 r1 = 2.over(5) + 3;              // You can use Rational!T like T.
17 
18 import std.bigint;
19 Rational!BigInt rb = 10.over(33);// You can use BigInt as T.
20 rb ^^= -10;
21 assert(rb == Rational!BigInt(BigInt(33)^^10, BigInt(10)^^10));

If T can be operated in pure nothrow @safe function, Rational!T can be too.

1 void foo() pure nothrow @safe
2 {
3     auto r = rational(1, 3);    //int is pure nothrow @safe type
4     r += 3.over(4);
5     ...
6 }

You can use "%(...%)" format when formatted write. Where inner format "..." can be T's format, first one is numerator's format, second is denominator's format.

1 import std.format;
2 
3 void main(){
4     auto writer = appender!string;
5 
6     formattedWrite(writer, "%(%04d / %04d%)", rational(10, 33));
7     assert(writer.data == "0010 / 0033");
8 
9     writer = appender!string;
10     formattedWrite(writer, "%(den : %2$s , num : %1$s%)", rational(10, 33));
11     assert(writer.data == "den : 33 , num : 10");
12 
13     writer = appender!string;
14     formattedWrite(writer, "%04d", rational(10, 30));
15     assert(writer.data == "0010/0030");
16 }