is this invalid code

[Daniel Davidson]

The following crashes on writeln, but looks reasonable. Is some 
form of initializing ctor required for RateCurve?

import std.datetime;
import std.range;
import std.stdio;

struct DateRate {
   Date date;
   double value = 0.0;
}

struct RateCurve {
   private immutable(DateRate)[] _data;
}

struct CFS {
   double initialValue;
   RateCurve growth;
}

void main() {
   auto s = CFS(1.0);
   // auto s = CFS(1.0, RateCurve()); // crashes
   // auto s = CFS(1.0, RateCurve([])); // works
   writeln(s);
}

Thanks
Dan