import std.stdio : writeln; import std.conv : to; class Fib(T) if (__traits(isIntegral, T)) { T opIndex(T n) const pure nothrow @trusted @nogc in { assert(n > 0); } body { T y; { T x = 1; foreach (_; 0..n) (((x = n = x) += y) ? y : y) = n;…